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The [[wp:Knuth shuffle|Knuth shuffle]] (a.k.a. the Fisher-Yates shuffle) is an algorithm for randomly shuffling the elements of an array.

Implement the Knuth shuffle for an integer array (or, if possible, an array of any type).

Given an array '''''items''''' with indices ranging from ''0'' to '''''last''''', the algorithm can be defined as follows (pseudo-code):

'''for''' ''i'' '''from''' ''last'' '''downto''' 1 '''do''': '''let''' ''j'' = random integer in range ''0'' $\leq$ ''j'' $\leq$ ''i'' '''swap''' ''items''[''i''] '''with''' ''items''[''j'']

Notes:

• It modifies the input array in-place. If that is unreasonable in your programming language, you may amend the algorithm to return the shuffled items as a new array instead.
• The algorithm can also be amended to iterate from left to right, if that is more convenient.

{| class="wikitable" |- ! Input array ! Possible output arrays |- | [] | [] |- | [10] | [10] |- | [10, 20] | [10, 20] [20, 10] |- | [10, 20, 30] | [10, 20, 30] [10, 30, 20] [20, 10, 30] [20, 30, 10] [30, 10, 20] [30, 20, 10] |}

(These are listed here just for your convenience; no need to demonstrate them on the page.)

• [[Sattolo cycle]]

360 Assembly

{{trans|BBC BASIC}}


*        Knuth shuffle             02/11/2015
KNUTHSH  CSECT
USING  KNUTHSH,R15
LA     R6,1               i=1
LOOPI1   C      R6,=A(CARDS)       do i=1 to cards
BH     ELOOPI1
STC    R6,PACK(R6)        pack(i)=i
LA     R6,1(R6)           i=i+1
B      LOOPI1
ELOOPI1  LA     R7,CARDS           n=cards
LOOPN    C      R7,=F'2'           do n=cards to 2 by -1
BL     ELOOPN
L      R5,RANDSEED        r5=seed
M      R4,=F'397204094'   r4r5=seed*const
D      R4,=X'7FFFFFFF'    r5=r5 div (2^31-1)
ST     R4,RANDSEED        r4=r5 mod (2^31-1); seed=r4
LR     R5,R4              r5=seed
LA     R4,0               r4=0
DR     R4,R7              r5=seed div n; r4=seed mod n
LA     R9,1(R4)           r2=randint(n)+1 [1:n]
LA     R4,PACK(R7)        @pack(n)
LA     R5,PACK(R9)        @pack(nw)
MVC    TMP,0(R4)          tmp=pack(n)
MVC    0(1,R4),0(R5)      pack(n)=pack(nw)
MVC    0(1,R5),TMP        pack(nw)=tmp
BCTR   R7,0               n=n-1
B      LOOPN
ELOOPN   LA     R6,1               i=1
LA     R8,PG              pgi=@pg
LOOPI2   C      R6,=A(CARDS)       do i=1 to cards
BH     ELOOPI2
XR     R2,R2              r2=0
IC     R2,PACK(R6)        pack(i)
XDECO  R2,XD              edit pack(i)
MVC    0(3,R8),XD+9       output pack(i)
LA     R8,3(R8)           pgi=pgi+3
LA     R6,1(R6)           i=i+1
B      LOOPI2
ELOOPI2  XPRNT  PG,80              print buffer
XR     R15,R15            set return code
CARDS    EQU    20                 number of cards
PACK     DS     (CARDS+1)C         pack of cards
TMP      DS     C                  temp for swap
PG       DC     CL80' '            buffer
XD       DS     CL12               to decimal
RANDSEED DC     F'16807'           running seed
YREGS
END    KNUTHSH



{{out}}


13 16 10 18 19 14  6 17  2  5  1 15  7 11 12  9  8 20  4  3



ACL2

:set-state-ok t

(defun array-swap (name array i j)
(let ((ai (aref1 name array i))
(aj (aref1 name array j)))
(aset1 name
(aset1 name array j ai)
i aj)))

(defun shuffle-r (name array m state)
(if (zp m)
(mv array state)
(mv-let (i state)
(randomm state) (shuffle-r name (array-swap name array i m) (1- m) state)))) (defun shuffle (name array state) (shuffle-r name array (1- (first (dimensions name array))) state))  Ada This implementation is a generic shuffle routine, able to shuffle an array of any type. generic type Element_Type is private; type Array_Type is array (Positive range <>) of Element_Type; procedure Generic_Shuffle (List : in out Array_Type);  with Ada.Numerics.Discrete_Random; procedure Generic_Shuffle (List : in out Array_Type) is package Discrete_Random is new Ada.Numerics.Discrete_Random(Result_Subtype => Integer); use Discrete_Random; K : Integer; G : Generator; T : Element_Type; begin Reset (G); for I in reverse List'Range loop K := (Random(G) mod I) + 1; T := List(I); List(I) := List(K); List(K) := T; end loop; end Generic_Shuffle;  An example using Generic_Shuffle. with Ada.Text_IO; with Generic_Shuffle; procedure Test_Shuffle is type Integer_Array is array (Positive range <>) of Integer; Integer_List : Integer_Array := (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18); procedure Integer_Shuffle is new Generic_Shuffle(Element_Type => Integer, Array_Type => Integer_Array); begin for I in Integer_List'Range loop Ada.Text_IO.Put(Integer'Image(Integer_List(I))); end loop; Integer_Shuffle(List => Integer_List); Ada.Text_IO.New_Line; for I in Integer_List'Range loop Ada.Text_IO.Put(Integer'Image(Integer_List(I))); end loop; end Test_Shuffle;  Aime The shuffle function works on any type (the lists are heterogenous). void shuffle(list l) { integer i; i = ~l; if (i) { i -= 1; while (i) { l.spin(i, drand(i)); i -= 1; } } }  ALGOL 68 {{works with|ALGOL 68G}} PROC between = (INT a, b)INT : ( ENTIER (random * ABS (b-a+1) + (a<b|a|b)) ); PROC knuth shuffle = (REF[]INT a)VOID: ( FOR i FROM LWB a TO UPB a DO INT j = between(LWB a, UPB a); INT t = a[i]; a[i] := a[j]; a[j] := t OD );  main:( [20]INT a; FOR i FROM 1 TO 20 DO a[i] := i OD; knuth shuffle(a); print(a) )  AppleScript Iteration set n to 25 set array to {} repeat with i from 1 to n set end of array to i end repeat copy {array, array} to {unshuffled, shuffled} repeat with i from n to 1 by -1 set j to (((random number) * (i - 1)) as integer) + 1 set shuffled's item i to array's item j if j ≠ i's contents then set array's item j to array's item i end repeat return {unshuffled, shuffled}  Example: {{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25}, {14, 25, 3, 1, 12, 18, 11, 20, 16, 15, 21, 5, 22, 19, 2, 24, 8, 10, 13, 6, 17, 23, 9, 7, 4}}  Functional composition -- KNUTH SHUFFLE ------------------------------------------------------------- -- knuthShuffle :: [a] -> [a] on knuthShuffle(xs) -- randomSwap :: [Int] -> Int -> [Int] script randomSwap on |λ|(a, i) if i > 1 then set iRand to random number from 1 to i tell a set tmp to item iRand set item iRand to item i set item i to tmp it end tell else a end if end |λ| end script foldr(randomSwap, xs, enumFromTo(1, length of xs)) end knuthShuffle -- TEST ---------------------------------------------------------------------- on run knuthShuffle(["alpha", "beta", "gamma", "delta", "epsilon", ¬ "zeta", "eta", "theta", "iota", "kappa", "lambda", "mu"]) end run -- GENERIC FUNCTIONS --------------------------------------------------------- -- enumFromTo :: Int -> Int -> [Int] on enumFromTo(m, n) if m > n then set d to -1 else set d to 1 end if set lst to {} repeat with i from m to n by d set end of lst to i end repeat return lst end enumFromTo -- foldr :: (a -> b -> a) -> a -> [b] -> a on foldr(f, startValue, xs) tell mReturn(f) set v to startValue set lng to length of xs repeat with i from lng to 1 by -1 set v to |λ|(v, item i of xs, i, xs) end repeat return v end tell end foldr -- Lift 2nd class handler function into 1st class script wrapper -- mReturn :: Handler -> Script on mReturn(f) if class of f is script then f else script property |λ| : f end script end if end mReturn  {{Out}} e.g. {"mu", "theta", "alpha", "delta", "zeta", "gamma", "iota", "kappa", "lambda", "epsilon", "beta", "eta"}  ARM Assembly {{works with|as|Raspberry Pi}}  /* ARM assembly Raspberry PI */ /* program knuthShuffle.s */ /************************************/ /* Constantes */ /************************************/ .equ STDOUT, 1 @ Linux output console .equ EXIT, 1 @ Linux syscall .equ WRITE, 4 @ Linux syscall /*********************************/ /* Initialized data */ /*********************************/ .data sMessResult: .ascii "Value : " sMessValeur: .fill 11, 1, ' ' @ size => 11 szCarriageReturn: .asciz "\n" .align 4 iGraine: .int 123456 .equ NBELEMENTS, 10 TableNumber: .int 1,2,3,4,5,6,7,8,9,10 /*********************************/ /* UnInitialized data */ /*********************************/ .bss /*********************************/ /* code section */ /*********************************/ .text .global main main: @ entry of program ldr r0,iAdrTableNumber @ address number table mov r1,#NBELEMENTS @ number of élements bl knuthShuffle ldr r2,iAdrTableNumber mov r3,#0 1: @ loop display table ldr r0,[r2,r3,lsl #2] ldr r1,iAdrsMessValeur @ display value bl conversion10 @ call function ldr r0,iAdrsMessResult bl affichageMess @ display message add r3,#1 cmp r3,#NBELEMENTS - 1 ble 1b ldr r0,iAdrszCarriageReturn bl affichageMess /* 2e shuffle */ ldr r0,iAdrTableNumber @ address number table mov r1,#NBELEMENTS @ number of élements bl knuthShuffle ldr r2,iAdrTableNumber mov r3,#0 2: @ loop display table ldr r0,[r2,r3,lsl #2] ldr r1,iAdrsMessValeur @ display value bl conversion10 @ call function ldr r0,iAdrsMessResult bl affichageMess @ display message add r3,#1 cmp r3,#NBELEMENTS - 1 ble 2b 100: @ standard end of the program mov r0, #0 @ return code mov r7, #EXIT @ request to exit program svc #0 @ perform the system call iAdrsMessValeur: .int sMessValeur iAdrszCarriageReturn: .int szCarriageReturn iAdrsMessResult: .int sMessResult iAdrTableNumber: .int TableNumber /******************************************************************/ /* Knuth Shuffle */ /******************************************************************/ /* r0 contains the address of table */ /* r1 contains the number of elements */ knuthShuffle: push {r2-r5,lr} @ save registers mov r5,r0 @ save table address mov r2,#0 @ start index 1: mov r0,r2 @ generate aleas bl genereraleas ldr r3,[r5,r2,lsl #2] @ swap number on the table ldr r4,[r5,r0,lsl #2] str r4,[r5,r2,lsl #2] str r3,[r5,r0,lsl #2] add r2,#1 @ next number cmp r2,r1 @ end ? blt 1b @ no -> loop 100: pop {r2-r5,lr} bx lr @ return /******************************************************************/ /* display text with size calculation */ /******************************************************************/ /* r0 contains the address of the message */ affichageMess: push {r0,r1,r2,r7,lr} @ save registres mov r2,#0 @ counter length 1: @ loop length calculation ldrb r1,[r0,r2] @ read octet start position + index cmp r1,#0 @ if 0 its over addne r2,r2,#1 @ else add 1 in the length bne 1b @ and loop @ so here r2 contains the length of the message mov r1,r0 @ address message in r1 mov r0,#STDOUT @ code to write to the standard output Linux mov r7, #WRITE @ code call system "write" svc #0 @ call systeme pop {r0,r1,r2,r7,lr} @ restaur des 2 registres */ bx lr @ return /******************************************************************/ /* Converting a register to a decimal unsigned */ /******************************************************************/ /* r0 contains value and r1 address area */ /* r0 return size of result (no zero final in area) */ /* area size => 11 bytes */ .equ LGZONECAL, 10 conversion10: push {r1-r4,lr} @ save registers mov r3,r1 mov r2,#LGZONECAL 1: @ start loop bl divisionpar10U @unsigned r0 <- dividende. quotient ->r0 reste -> r1 add r1,#48 @ digit strb r1,[r3,r2] @ store digit on area cmp r0,#0 @ stop if quotient = 0 subne r2,#1 @ else previous position bne 1b @ and loop @ and move digit from left of area mov r4,#0 2: ldrb r1,[r3,r2] strb r1,[r3,r4] add r2,#1 add r4,#1 cmp r2,#LGZONECAL ble 2b @ and move spaces in end on area mov r0,r4 @ result length mov r1,#' ' @ space 3: strb r1,[r3,r4] @ store space in area add r4,#1 @ next position cmp r4,#LGZONECAL ble 3b @ loop if r4 <= area size 100: pop {r1-r4,lr} @ restaur registres bx lr @return /***************************************************/ /* division par 10 unsigned */ /***************************************************/ /* r0 dividende */ /* r0 quotient */ /* r1 remainder */ divisionpar10U: push {r2,r3,r4, lr} mov r4,r0 @ save value //mov r3,#0xCCCD @ r3 <- magic_number lower raspberry 3 //movt r3,#0xCCCC @ r3 <- magic_number higter raspberry 3 ldr r3,iMagicNumber @ r3 <- magic_number raspberry 1 2 umull r1, r2, r3, r0 @ r1<- Lower32Bits(r1*r0) r2<- Upper32Bits(r1*r0) mov r0, r2, LSR #3 @ r2 <- r2 >> shift 3 add r2,r0,r0, lsl #2 @ r2 <- r0 * 5 sub r1,r4,r2, lsl #1 @ r1 <- r4 - (r2 * 2) = r4 - (r0 * 10) pop {r2,r3,r4,lr} bx lr @ leave function iMagicNumber: .int 0xCCCCCCCD /***************************************************/ /* Generation random number */ /***************************************************/ /* r0 contains limit */ genereraleas: push {r1-r4,lr} @ save registers ldr r4,iAdriGraine ldr r2,[r4] ldr r3,iNbDep1 mul r2,r3,r2 ldr r3,iNbDep1 add r2,r2,r3 str r2,[r4] @ maj de la graine pour l appel suivant cmp r0,#0 beq 100f mov r1,r0 @ divisor mov r0,r2 @ dividende bl division mov r0,r3 @ résult = remainder 100: @ end function pop {r1-r4,lr} @ restaur registers bx lr @ return /*****************************************************/ iAdriGraine: .int iGraine iNbDep1: .int 0x343FD iNbDep2: .int 0x269EC3 /***************************************************/ /* integer division unsigned */ /***************************************************/ division: /* r0 contains dividend */ /* r1 contains divisor */ /* r2 returns quotient */ /* r3 returns remainder */ push {r4, lr} mov r2, #0 @ init quotient mov r3, #0 @ init remainder mov r4, #32 @ init counter bits b 2f 1: @ loop movs r0, r0, LSL #1 @ r0 <- r0 << 1 updating cpsr (sets C if 31st bit of r0 was 1) adc r3, r3, r3 @ r3 <- r3 + r3 + C. This is equivalent to r3 ? (r3 << 1) + C cmp r3, r1 @ compute r3 - r1 and update cpsr subhs r3, r3, r1 @ if r3 >= r1 (C=1) then r3 <- r3 - r1 adc r2, r2, r2 @ r2 <- r2 + r2 + C. This is equivalent to r2 <- (r2 << 1) + C 2: subs r4, r4, #1 @ r4 <- r4 - 1 bpl 1b @ if r4 >= 0 (N=0) then loop pop {r4, lr} bx lr  AutoHotkey ahk forum: [http://www.autohotkey.com/forum/viewtopic.php?t=44657&postdays=0&postorder=asc&start=133 discussion] MsgBox % shuffle("1,2,3,4,5,6,7,8,9") MsgBox % shuffle("1,2,3,4,5,6,7,8,9") shuffle(list) { ; shuffle comma separated list, converted to array StringSplit a, list, , ; make array (length = a0) Loop % a0-1 { Random i, A_Index, a0 ; swap item 1,2... with a random item to the right of it t := a%i%, a%i% := a%A_Index%, a%A_Index% := t } Loop % a0 ; construct string from sorted array s .= "," . a%A_Index% Return SubStr(s,2) ; drop leading comma }  AutoIt  Dima[10]
ConsoleWrite('array before permutation:' & @CRLF)
For $i = 0 To 9$a[$i] = Random(20,100,1) ConsoleWrite($a[$i] & ' ') Next ConsoleWrite(@CRLF) _Permute($a)
ConsoleWrite('array after permutation:' & @CRLF)
For $i = 0 To UBound($a) -1
ConsoleWrite($a[$i] & ' ')
Next
ConsoleWrite(@CRLF)

Func _Permute(ByRef $array) Local$random, $tmp For$i = UBound($array) -1 To 0 Step -1$random = Random(0,$i,1)$tmp = $array[$random]
$array[$random] = $array[$i]
$array[$i] = $tmp Next EndFunc  {{out}}  array before permutation: 43 57 37 20 97 98 69 76 97 70 array after permutation: 57 69 97 70 37 97 20 76 43 98  AWK Many [[Arrays#AWK|arrays in AWK]] have the first index at 1. This example shows how to shuffle such arrays. The elements can be integers, floating-point numbers, or strings. # Shuffle an _array_ with indexes from 1 to _len_. function shuffle(array, len, i, j, t) { for (i = len; i > 1; i--) { # j = random integer from 1 to i j = int(i * rand()) + 1 # swap array[i], array[j] t = array[i] array[i] = array[j] array[j] = t } } # Test program. BEGIN { len = split("11 22 33 44 55 66 77 88 99 110", array) shuffle(array, len) for (i = 1; i < len; i++) printf "%s ", array[i] printf "%s\n", array[len] }  BASIC RANDOMIZE TIMER DIM cards(51) AS INTEGER DIM L0 AS LONG, card AS LONG PRINT "before:" FOR L0 = 0 TO 51 cards(L0) = L0 PRINT LTRIM$(STR$(cards(L0))); " "; NEXT FOR L0 = 51 TO 0 STEP -1 card = INT(RND * (L0 + 1)) IF card <> L0 THEN SWAP cards(card), cards(L0) NEXT PRINT : PRINT "after:" FOR L0 = 0 TO 51 PRINT LTRIM$(STR$(cards(L0))); " "; NEXT PRINT  {{out}}  before: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 after: 27 14 37 35 3 44 25 38 46 1 22 49 2 51 16 32 20 30 4 33 36 6 31 21 41 34 9 13 0 50 47 48 40 39 7 18 19 26 24 10 29 5 12 28 11 17 43 45 8 23 42 15  = Applesoft BASIC = As mentioned in the Sinclair ZX81 BASIC solution, for very small positive integer values, a string is a much more memory-efficient array, but here is an example of an array with numbers. Line 150 initializes and prints each element in the array. Line 190 performs the swap of the elements.  100 : 110 REM KNUTH SHUFFLE 120 : 130 DIM A(25) 140 FOR I = 1 TO 25 150 A(I) = I: PRINT A(I);" ";: NEXT I 160 PRINT : PRINT 170 FOR I = 25 TO 2 STEP - 1 180 J = INT ( RND (1) * I + 1) 190 T = A(I):A(I) = A(J):A(J) = T: NEXT I 200 FOR I = 1 TO 25 210 PRINT A(I);" ";: NEXT I 220 END  {{out}} 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 7 18 19 20 21 22 23 24 25  When it has finished, the screen will show (for example): 20 5 6 9 15 23 22 8 4 24 7 11 16 21 2 17 14 10 19 13 12 18 1 3 25  = Sinclair ZX81 BASIC = For very small positive integer values, a string (which can be treated as an array of bytes) is much more memory-efficient than an array of numbers. In this program we shuffle a string consisting of the letters 'A' to 'Z'. The ZX81 is slow enough that we can watch the shuffle happening in real time, with items switching to inverse video display as they are shuffled. (This can be done, in the ZX81 character set, by setting the high bit in the character code.) Line 10 seeds the pseudo-random number generator. Note that strings (and arrays) are indexed from 1. The program works with the unexpanded (1k RAM) ZX81.  10 RAND 20 LET A$=""
30 FOR I=1 TO 26
40 LET A$=A$+CHR$(37+I) 50 NEXT I 60 PRINT A$
70 FOR I=26 TO 2 STEP -1
80 LET J=1+INT (RND*I)
90 LET T$=A$(I)
100 LET A$(I)=A$(J)
110 LET A$(J)=T$
120 PRINT AT 0,I-1;CHR$(CODE A$(I)+128)
130 PRINT AT 0,J-1;CHR$(CODE A$(J)+128)
140 NEXT I


{{out}} While the program is running, we will see something like this (using lower case as a stand-in for inverse video):

ABCuEFGzwJKLMNOPxySvdtiqrh


When it has finished, the screen will show (for example):

lcjbpxekzsaygumwnovfdtiqrh


BBC BASIC

      cards% = 52
DIM pack%(cards%)
FOR I% = 1 TO cards%
pack%(I%) = I%
NEXT I%
FOR N% = cards% TO 2 STEP -1
SWAP pack%(N%),pack%(RND(N%))
NEXT N%
FOR I% = 1 TO cards%
PRINT pack%(I%);
NEXT I%
PRINT


== {{header|bc}} == I provide a shuffle() function. It can only shuffle an array of numbers. It fails if the array has more than 32768 elements. It always shuffles the array named shuffle[]; the array is not a function parameter because bc passes arrays by copying.

This code requires a bc with long names; the test program also requires a bc with the print statement. {{works with|OpenBSD bc}}

seed = 1   /* seed of the random number generator */
scale = 0

/* Random number from 0 to 32767. */
define rand() {
/* Formula (from POSIX) for random numbers of low quality. */
seed = (seed * 1103515245 + 12345) % 4294967296
return ((seed / 65536) % 32768)
}

/* Shuffle the first _count_ elements of shuffle[]. */
define shuffle(count) {
auto b, i, j, t

i = count
while (i > 0) {
/* j = random number in [0, i) */
b = 32768 % i  /* want rand() >= b */
while (1) {
j = rand()
if (j >= b) break
}
j = j % i

/* decrement i, swap shuffle[i] and shuffle[j] */
t = shuffle[--i]
shuffle[i] = shuffle[j]
shuffle[j] = t
}
}

/* Test program. */
define print_array(count) {
auto i
for (i = 0; i < count - 1; i++) print shuffle[i], ", "
print shuffle[i], "\n"
}

for (i = 0; i < 10; i++) shuffle[i] = 11 * (i + 1)
"Original array: "; trash = print_array(10)

trash = shuffle(10)
"Shuffled array: "; trash = print_array(10)
quit


{{out}}

Original array: 11, 22, 33, 44, 55, 66, 77, 88, 99, 110
Shuffled array: 66, 44, 11, 55, 33, 77, 110, 22, 88, 99


Brat

shuffle = { a |
(a.length - 1).to 1 { i |
random_index = random(0, i)
temp = a[i]
a[i] = a[random_index]
a[random_index] = temp
}

a
}

p shuffle [1 2 3 4 5 6 7]


C

This shuffles any "object"; it imitates qsort in the syntax.

#include <iostream>
#include <string.h>

int rrand(int m)
{
return (int)((double)m * ( rand() / (RAND_MAX+1.0) ));
}

#define BYTE(X) ((unsigned char *)(X))
void shuffle(void *obj, size_t nmemb, size_t size)
{
void *temp = malloc(size);
size_t n = nmemb;
while ( n > 1 ) {
size_t k = rrand(n--);
memcpy(temp, BYTE(obj) + n*size, size);
memcpy(BYTE(obj) + n*size, BYTE(obj) + k*size, size);
memcpy(BYTE(obj) + k*size, temp, size);
}
free(temp);
}


Alternatively, using Durstenfeld's method (swapping selected item and last item in each iteration instead of literally shifting everything), and macro'd function declaration/definition:

#include <stdio.h>
#include <stdlib.h>

/* define a shuffle function. e.g. decl_shuffle(double).
* advantage: compiler is free to optimize the swap operation without
*            indirection with pointers, which could be much faster.
* disadvantage: each datatype needs a separate instance of the function.
*            for a small funciton like this, it's not very big a deal.
*/
#define decl_shuffle(type)				\
void shuffle_##type(type *list, size_t len) {		\
int j;						\
type tmp;					\
while(len) {					\
j = irand(len);				\
if (j != len - 1) {			\
tmp = list[j];			\
list[j] = list[len - 1];	\
list[len - 1] = tmp;		\
}					\
len--;					\
}						\
}							\

/* random integer from 0 to n-1 */
int irand(int n)
{
int r, rand_max = RAND_MAX - (RAND_MAX % n);
/* reroll until r falls in a range that can be evenly
* distributed in n bins.  Unless n is comparable to
* to RAND_MAX, it's not *that* important really. */
while ((r = rand()) >= rand_max);
return r / (rand_max / n);
}

/* declare and define int type shuffle function from macro */
decl_shuffle(int);

int main()
{
int i, x[20];

for (i = 0; i < 20; i++) x[i] = i;
for (printf("before:"), i = 0; i < 20 || !printf("\n"); i++)
printf(" %d", x[i]);

shuffle_int(x, 20);

for (printf("after: "), i = 0; i < 20 || !printf("\n"); i++)
printf(" %d", x[i]);
return 0;
}


C++

'''Compiler:''' [[g++]] (version 4.3.2 20081105 (Red Hat 4.3.2-7))

#include <cstdlib>
#include <algorithm>
#include <iterator>

template<typename RandomAccessIterator>
void knuthShuffle(RandomAccessIterator begin, RandomAccessIterator end) {
for(unsigned int n = end - begin - 1; n >= 1; --n) {
unsigned int k = rand() % (n + 1);
if(k != n) {
std::iter_swap(begin + k, begin + n);
}
}
}


The standard library provides this in the form of std::random_shuffle.

#include <algorithm>
#include <vector>

int main()
{
int array[] = { 1,2,3,4,5,6,7,8,9 }; // C-style array of integers
std::vector<int> vec(array, array + 9); // build STL container from int array

std::random_shuffle(array, array + 9); // shuffle C-style array
std::random_shuffle(vec.begin(), vec.end()); // shuffle STL container
}


C#

(T[] array)
{
System.Random random = new System.Random();
for (int i = 0; i < array.Length; i++)
{
int j = random.Next(i, array.Length); // Don't select from the entire array on subsequent loops
T temp = array[i]; array[i] = array[j]; array[j] = temp;
}
}


Clojure

(defn shuffle [vect]
(reduce (fn [v i] (let [r (rand-int i)]
(assoc v i (v r) r (v i))))
vect (range (dec (count vect)) 1 -1)))


This works by generating a sequence of end-indices from n-1 to 1, then reducing that sequence (starting with the original vector) through a function that, given a vector and end-index, performs a swap between the end-index and some random index less than the end-index.

COBOL

       IDENTIFICATION DIVISION.
PROGRAM-ID. knuth-shuffle.

DATA DIVISION.
LOCAL-STORAGE SECTION.
01  i                       PIC 9(8).
01  j                       PIC 9(8).

01  temp                    PIC 9(8).

78  Table-Len               VALUE 10.
01  ttable-area.
03  ttable              PIC 9(8) OCCURS Table-Len TIMES.

PROCEDURE DIVISION USING ttable-area.
MOVE FUNCTION RANDOM(FUNCTION CURRENT-DATE (11:6)) TO i

PERFORM VARYING i FROM Table-Len BY -1 UNTIL i = 0
COMPUTE j =
FUNCTION MOD(FUNCTION RANDOM * 10000, Table-Len) + 1

MOVE ttable (i) TO temp
MOVE ttable (j) TO ttable (i)
MOVE temp TO ttable (j)
END-PERFORM

GOBACK
.


CMake

# shuffle(<output variable> [<value>...]) shuffles the values, and
# stores the result in a list.
function(shuffle var)
set(forever 1)

# Receive ARGV1, ARGV2, ..., ARGV${last} as an array of values. math(EXPR last "${ARGC} - 1")

# Shuffle the array with Knuth shuffle (Fisher-Yates shuffle).
foreach(i RANGE ${last} 1) # Roll j = a random number from 1 to i. math(EXPR min "100000000 %${i}")
while(forever)
string(RANDOM LENGTH 8 ALPHABET 0123456789 j)
if(NOT j LESS min)        # Prevent modulo bias when j < min.
break()                 # Break loop when j >= min.
endif()
endwhile()
math(EXPR j "${j} %${i} + 1")

# Swap ARGV${i} with ARGV${j}.
set(t ${ARGV${i}})
set(ARGV${i}${ARGV${j}}) set(ARGV${j} ${t}) endforeach(i) # Convert array to list. set(answer) foreach(i RANGE 1${last})
list(APPEND answer ${ARGV${i}})
endforeach(i)
set("${var}"${answer} PARENT_SCOPE)
endfunction(shuffle)

shuffle(result 11 22 33 44 55 66)
message(STATUS "${result}") # One possible output: # -- 66;33;22;55;44;11  CoffeeScript {{trans|JavaScript}} knuth_shuffle = (a) -> n = a.length while n > 1 r = Math.floor(n * Math.random()) n -= 1 [a[n], a[r]] = [a[r], a[n]] a counts = "1,2,3": 0 "1,3,2": 0 "2,1,3": 0 "2,3,1": 0 "3,1,2": 0 "3,2,1": 0 for i in [1..100000] counts[knuth_shuffle([ 1, 2, 3 ]).join(",")] += 1 for key, val of counts console.log "#{key}: #{val}"  {{out}}  > coffee knuth_shuffle.coffee 1,2,3: 16714 1,3,2: 16566 2,1,3: 16460 2,3,1: 16715 3,1,2: 16750 3,2,1: 16795  Common Lisp (defun nshuffle (sequence) (loop for i from (length sequence) downto 2 do (rotatef (elt sequence (random i)) (elt sequence (1- i)))) sequence)  This operates on arbitrary sequences, but will be inefficient applied to a list as opposed to a vector. Dispatching on type, and using an intermediate vector to hold the contents of list can make both cases more efficient (since the array specific case can use aref rather than elt): (defun nshuffle (sequence) (etypecase sequence (list (nshuffle-list sequence)) (array (nshuffle-array sequence)))) (defun nshuffle-list (list) "Shuffle the list using an intermediate vector." (let ((array (nshuffle-array (coerce list 'vector)))) (declare (dynamic-extent array)) (map-into list 'identity array))) (defun nshuffle-array (array) (loop for i from (length array) downto 2 do (rotatef (aref array (random i)) (aref array (1- i))) finally (return array)))  Crystal def knuthShuffle(items : Array) i = items.size-1 while i > 1 j = Random.rand(0..i) items.swap(i, j) i -= 1 end end  D Standard Version A variant of the Knuth shuffle is in the D standard library Phobos: void main() { import std.stdio, std.random; auto a = [1, 2, 3, 4, 5, 6, 7, 8, 9]; a.randomShuffle; a.writeln; }  {{out}} [8, 9, 3, 1, 7, 5, 4, 6, 2]  One Implementation This shuffles any collection that supports random access, length and swapping of items: import std.stdio, std.algorithm, std.random, std.range; void knuthShuffle(Range)(Range r) if (isRandomAccessRange!Range && hasLength!Range && hasSwappableElements!Range) { foreach_reverse (immutable i, ref ri; r[1 ..$ - 1])
ri.swap(r[uniform(0, i + 1)]);
}

void main() {
auto a = [1, 2, 3, 4, 5, 6, 7, 8, 9];
a.knuthShuffle;
a.writeln;
}


Delphi

''See [[Knuth_shuffle#Pascal|Pascal]] or [[Knuth_shuffle#DWScript|DWScript]]''

DWScript

procedure KnuthShuffle(a : array of Integer);
var
i, j, tmp : Integer;
begin
for i:=a.High downto 1 do begin
j:=RandomInt(a.Length);
tmp:=a[i]; a[i]:=a[j]; a[j]:=tmp;
end;
end;


E

def shuffle(array, random) {
for bound in (2..(array.size())).descending() {
def i := random.nextInt(bound)
def swapTo := bound - 1
def t := array[swapTo]
array[swapTo] := array[i]
array[i] := t
}
}

? def arr := [1,2,3,4,5,6,7,8,9,10].diverge()
# value: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].diverge()

? shuffle(arr, entropy)
? arr
# value: [4, 5, 2, 9, 7, 8, 1, 3, 6, 10].diverge()


EchoLisp


Remark- The native '''shuffle''' function implementation  in EchoLisp has been replaced by this one.
Thx Rosetta Code.
(lib 'list) ;; for list-permute

;; use "inside-out" algorithm, no swapping needed.
;; returns a random permutation vector of [0 .. n-1]
(define (rpv n (j))
(define v (make-vector n))
(for [(i n)]
(set! j (random (1+ i)))
(when (!= i j) (vector-set! v i [v j]))
(vector-set! v j i))
v)

;; apply to any kind of list
(define (k-shuffle list)
(list-permute list (vector->list (rpv (length list)))))

;; out
(k-shuffle (iota 17))
→ (16 7 11 10 0 9 15 12 13 8 4 2 14 3 6 5 1)

(k-shuffle
'(adrien 🎸 alexandre 🚂  antoine  🍼 ben 📚   georges 📷   julie 🎥 marine 🐼 nathalie 🍕 ))
→ (marine alexandre 🎥 julie 🎸 ben 🍼 nathalie 📚 georges 🚂 antoine adrien 🐼 📷 🍕)

(shuffle ;; native
'(adrien 🎸 alexandre 🚂 antoine 🍼 ben 📚 georges 📷 julie 🎥 marine 🐼 nathalie 🍕 ))
→ (antoine 🎥 🚂 marine adrien nathalie 🍼 🍕 ben 🐼 julie 📷 📚 🎸 alexandre georges)



Egel


import "prelude.eg"
import "random.ego"

using System
using List
using Math

def swap =
[ I J XX -> insert I (nth J XX) (insert J (nth I XX) XX) ]

def shuffle =
[ XX ->
let INDICES = reverse (fromto 0 ((length XX) - 1)) in
let SWAPS = map [ I -> I (between 0 I) ] INDICES in
foldr [I J -> swap I J] XX SWAPS ]

def main = shuffle (fromto 1 9)



Eiffel


class
APPLICATION

create
make

feature {NONE} -- Initialization

make
do
test := <<1, 2>>
io.put_string ("Initial: ")
across
test as t
loop
io.put_string (t.item.out + " ")
end
test := shuffle (test)
io.new_line
io.put_string ("Shuffled: ")
across
test as t
loop
io.put_string (t.item.out + " ")
end
end

test: ARRAY [INTEGER]

shuffle (ar: ARRAY [INTEGER]): ARRAY [INTEGER]
-- Array containing the same elements as 'ar' in a shuffled order.
require
more_than_one_element: ar.count > 1
local
count, j, ith: INTEGER
random: V_RANDOM
do
create random
create Result.make_empty
Result.deep_copy (ar)
count := ar.count
across
1 |..| count as c
loop
j := random.bounded_item (c.item, count)
ith := Result [c.item]
Result [c.item] := Result [j]
Result [j] := ith
random.forth
end
ensure
same_elements: across ar as a all Result.has (a.item) end
end

end

</lang >
{{out}}

txt

Initial: 1 2 3 4 5 6 7
Shuffeld: 1 5 3 4 7 6 2



Elena

ELENA 4.x:

import system'routines;
import extensions;

const int MAX = 10;

extension randomOp
{
randomize()
{
var max := self.Length;

for(int i := 0, i < max, i += 1)
{
var j := randomGenerator.eval(i,max);

self.exchange(i,j)
};

^ self
}
}

public program()
{
var a := Array.allocate:MAX.populate:(i => i );

console.printLine(a.randomize())
}


{{out}}


7,3,6,8,4,9,0,1,2,5



Elixir

{{trans|Erlang}}

defmodule Knuth do
def shuffle( inputs ) do
n = length( inputs )
{[], acc} = Enum.reduce( n..1, {inputs, []}, &random_move/2 )
acc
end

defp random_move( n, {inputs, acc} ) do
item = Enum.at( inputs, :rand.uniform(n)-1 )
{List.delete( inputs, item ), [item | acc]}
end
end

seq = Enum.to_list( 0..19 )
IO.inspect Knuth.shuffle( seq )

seq = [1,2,3]
Enum.reduce(1..100000, Map.new, fn _,acc ->
k = Knuth.shuffle(seq)
Map.update(acc, k, 1, &(&1+1))
end)
|> Enum.each(fn {k,v} -> IO.inspect {k,v} end)


{{out}}


[17, 13, 4, 2, 16, 1, 8, 19, 9, 12, 14, 5, 0, 11, 6, 10, 18, 3, 15, 7]
{[1, 2, 3], 16702}
{[1, 3, 2], 16635}
{[2, 1, 3], 16518}
{[2, 3, 1], 16935}
{[3, 1, 2], 16500}
{[3, 2, 1], 16710}



Erlang


-module( knuth_shuffle ).

-export( [list/1] ).

list( Inputs ) ->
N = erlang:length( Inputs ),
{[], Acc} = lists:foldl( fun random_move/2, {Inputs, []}, lists:reverse(lists:seq(1, N)) ),
Acc.

random_move( N, {Inputs, Acc} ) ->
Item = lists:nth( random:uniform(N), Inputs ),
{lists:delete(Item, Inputs), [Item | Acc]}.



{{out}}


21> knuth_shuffle:list(lists:seq(1,9)).
[5,7,8,1,4,2,3,9,6]



ERRE

PROGRAM KNUTH_SHUFFLE

CONST CARDS%=52

DIM PACK%[CARDS%]

BEGIN
RANDOMIZE(TIMER)
FOR I%=1 TO CARDS% DO
PACK%[I%]=I%
END FOR
FOR N%=CARDS% TO 2 STEP -1 DO
SWAP(PACK%[N%],PACK%[1+INT(N%*RND(1))])
END FOR
FOR I%=1 TO CARDS% DO
PRINT(PACK%[I%];)
END FOR
PRINT
END PROGRAM



Euphoria

{{trans|BASIC}}

sequence cards
cards = repeat(0,52)
integer card,temp

puts(1,"Before:\n")
for i = 1 to 52 do
cards[i] = i
printf(1,"%d ",cards[i])
end for

for i = 52 to 1 by -1 do
card = rand(i)
if card != i then
temp = cards[card]
cards[card] = cards[i]
cards[i] = temp
end if
end for

puts(1,"\nAfter:\n")
for i = 1 to 52 do
printf(1,"%d ",cards[i])
end for


Factor

There is a randomize word already in the standard library. Implementation:

: randomize ( seq -- seq )
dup length [ dup 1 > ]
[ [ iota random ] [ 1 - ] bi [ pick exchange ] keep ]
while drop ;


Fantom

class Main
{
static Void knuthShuffle (List array)
{
((array.size-1)..1).each |Int i|
{
r := Int.random(0..i)
array.swap (i, r)
}
}

public static Void main ()
{
List a := [1,2,3,4,5]
knuthShuffle (a)
echo (a)

List b := ["apples", "oranges", "pears", "bananas"]
knuthShuffle (b)
echo (b)
}
}


Forth

include random.fs

: shuffle ( deck size -- )
2 swap do
dup i random cells +
over @ over @  swap
rot  ! over !
cell+
-1 +loop drop ;

: .array   0 do dup @ . cell+ loop drop ;

create deck 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ,

deck 10 2dup shuffle .array


Fortran

{{works with|Fortran|90 and later}}

program Knuth_Shuffle
implicit none

integer, parameter :: reps = 1000000
integer :: i, n
integer, dimension(10) :: a, bins = 0, initial = (/ (n, n=1,10) /)

do i = 1, reps
a = initial
call Shuffle(a)
where (a == initial) bins = bins + 1  ! skew tester
end do
write(*, "(10(i8))") bins
! prints  100382  100007   99783  100231  100507   99921   99941  100270  100290  100442

contains

subroutine Shuffle(a)
integer, intent(inout) :: a(:)
integer :: i, randpos, temp
real :: r

do i = size(a), 2, -1
call random_number(r)
randpos = int(r * i) + 1
temp = a(randpos)
a(randpos) = a(i)
a(i) = temp
end do

end subroutine Shuffle

end program Knuth_Shuffle


FreeBASIC

' version 22-10-2016
' compile with: fbc -s console
' for boundry checks on array's compile with: fbc -s console -exx

' sort from lower bound to the highter bound
' array's can have subscript range from -2147483648 to +2147483647

Sub knuth_down(a() As Long)

Dim As Long lb = LBound(a)
Dim As ULong n = UBound(a) - lb +1
Dim As ULong i, j

Randomize Timer

For i = n -1 To 1 Step -1
j =Fix(Rnd * (i +1))       ' 0 <= j <= i
Swap a(lb + i), a(lb + j)
Next

End Sub

Sub knuth_up(a() As Long)

Dim As Long lb = LBound(a)
Dim As ULong n = UBound(a) - lb +1
Dim As ULong i, j

Randomize Timer

For i = 0 To n -2
j = Fix(Rnd * (n - i) + i)   '  0 <= j < n-i, + i ==> i <= j < n
Swap a(lb + i), a(lb + j)
Next

End Sub

' ------=< MAIN >=------

Dim As Long i
Dim As Long array(1 To 52), array2(-7 To 7)

For i = 1 To 52 : array(i) = i : Next

Print "Starting array"
For i = 1 To 52
Print Using " ###";array(i);
Next : Print : Print

knuth_down(array())

Print "After Knuth shuffle downwards"
For i = 1 To 52
Print Using " ###";array(i);
Next : Print : Print

For i = LBound(array2) To UBound(array2)
array2(i) = i - LBound(array2) + 1
Next

Print "Starting array, first index <> 0 "
For i = LBound(array2) To UBound(array2)
Print Using " ##";array2(i);
Next : Print : Print

knuth_up(array2())
Print "After Knuth shuffle upwards"
For i = LBound(array2) To UBound(array2)
Print Using " ##";array2(i);
Next : Print : Print

' empty keyboard buffer
While InKey <> "" : Wend
Print : Print "hit any key to end program"
Sleep
End


{{out}}

Starting array
1   2   3   4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25
26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50
51  52

After Knuth shuffle downwards
2  17  46   4  40  36  51  24  19  29  13   9   8  16  44  43  47  34  14  52  39  35  23  31  48
42   7  12  21  33  18  32  22  49  38   6  27   1  41   5  20  15  37   3  28  30  26  45  50  25
10  11

Starting array, first index <> 0
1  2  3  4  5  6  7  8  9 10 11 12 13 14 15

After Knuth shuffle upwards
4  1  9 10 15 11 12  7  3  5  8 13  6 14  2


Frink

The built-in method array.shuffle[] implements the Fisher-Yates-Knuth shuffle algorithm:


a = [1,2,3]
a.shuffle[]



=={{header|F_Sharp|F#}}== Allows a shuffle of arrays of arbitrary items. Requires 2010 beta of F#. Lazily returns a sequence.

This is the original Fisher-Yates shuffle as described by the link:

open System

let FisherYatesShuffle (initialList : array<'a>) =                  // '
let availableFlags = Array.init initialList.Length (fun i -> (i, true))
// Which items are available and their indices
let rnd = new Random()
let nextItem nLeft =
let nItem = rnd.Next(0, nLeft)                              // Index out of available items
let index =                                                 // Index in original deck
availableFlags                                          // Go through available array
|> Seq.filter (fun (ndx,f) -> f)                        // and pick out only the available tuples
|> Seq.nth nItem                                        // Get the one at our chosen index
|> fst                                                  // and retrieve it's index into the original array
availableFlags.[index] <- (index, false)                    // Mark that index as unavailable
initialList.[index]                                         // and return the original item
seq {(initialList.Length) .. -1 .. 1}                           // Going from the length of the list down to 1
|> Seq.map (fun i -> nextItem i)                                // yield the next item


Here's the modified Knuth shuffle which shuffles the original array in place

let KnuthShuffle (lst : array<'a>) =                   // '
let Swap i j =                                                  // Standard swap
let item = lst.[i]
lst.[i] <- lst.[j]
lst.[j] <- item
let rnd = new Random()
let ln = lst.Length
[0..(ln - 2)]                                                   // For all indices except the last
|> Seq.iter (fun i -> Swap i (rnd.Next(i, ln)))                 // swap th item at the index with a random one following it (or itself)
lst                                                             // Return the list shuffled in place


Example:

 KnuthShuffle [| "Darrell"; "Marvin"; "Doug"; "Greg"; "Sam"; "Ken" |];;
val it : string array = [|"Marvin"; "Doug"; "Sam"; "Darrell"; "Ken"; "Greg"|]


FunL

def shuffle( a ) =
res = array( a )
n = a.length()

for i <- 0:n
r = rnd( i:n )
res(i), res(r) = res(r), res(i)

res.toList()


Gambas

'''[https://gambas-playground.proko.eu/?gist=58402023fbdc617ce10f6a85db721105 Click this link to run this code]'''

Public Sub Main()
Dim iTotal As Integer = 40
Dim iCount, iRand1, iRand2 As Integer
Dim iArray As New Integer[]

For iCount = 0 To iTotal
Next

Print "Original = ";
For iCount = 0 To iArray.Max
If iCount = iArray.max Then Print iArray[iCount]; Else Print iArray[iCount] & ",";
Next

For iCount = iTotal DownTo 0
iRand1 = Rand(iTotal)
iRand2 = Rand(iTotal)
Swap iArray[iRand1], iArray[iRand2]
Next

Print gb.NewLine & "Shuffled = ";
For iCount = 0 To iArray.Max
If iCount = iArray.max Then Print iArray[iCount]; Else Print iArray[iCount] & ",";
Next

End


Output:


Original = 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40
Shuffled = 8,23,12,31,4,38,39,40,37,34,14,0,21,22,3,10,27,26,17,15,6,7,19,2,24,35,25,16,18,36,1,13,32,33,20,5,9,11,29,28,30



GAP

# Return the list L after applying Knuth shuffle. GAP also has the function Shuffle, which does the same.
ShuffleAlt := function(a)
local i, j, n, t;
n := Length(a);
for i in [n, n - 1 .. 2] do
j := Random(1, i);
t := a[i];
a[i] := a[j];
a[j] := t;
od;
return a;
end;

# Return a "Permutation" object (a permutation of 1 .. n).
# They are printed in GAP, in cycle decomposition form.
PermShuffle := n -> PermList(ShuffleAlt([1 .. n]));

ShuffleAlt([1 .. 10]);
# [ 4, 7, 1, 5, 8, 2, 6, 9, 10, 3 ]

PermShuffle(10);
# (1,9)(2,3,6,4,5,10,8,7)

# One may also call the built-in random generator on the symmetric group :
Random(SymmetricGroup(10));
(1,8,2,5,9,6)(3,4,10,7)


Go

(Note, in addition to these examples, [https://golang.org/pkg/math/rand/#Shuffle rand.Shuffle] was added in [https://golang.org/doc/go1.10#math/rand Go1.10] implementing a Fisher–Yates shuffle.)

package main

import (
"fmt"
"math/rand"
"time"
)

func main() {
var a [20]int
for i := range a {
a[i] = i
}
fmt.Println(a)

rand.Seed(time.Now().UnixNano())
for i := len(a) - 1; i >= 1; i-- {
j := rand.Intn(i + 1)
a[i], a[j] = a[j], a[i]
}
fmt.Println(a)
}


To shuffle any type:

package main

import (
"fmt"
"math/rand"
"time"
)

// Generic Knuth Shuffle algorithm.  In Go, this is done with interface
// types.  The parameter s of function shuffle is an interface type.
// Any type satisfying the interface "shuffler" can be shuffled with
// this function.  Since the shuffle function uses the random number
// generator, it's nice to seed the generator at program load time.
func init() {
rand.Seed(time.Now().UnixNano())
}
func shuffle(s shuffler) {
for i := s.Len() - 1; i >= 1; i-- {
j := rand.Intn(i + 1)
s.Swap(i, j)
}
}

// Conceptually, a shuffler is an indexed collection of things.
// It requires just two simple methods.
type shuffler interface {
Len() int      // number of things in the collection
Swap(i, j int) // swap the two things indexed by i and j
}

// ints is an example of a concrete type implementing the shuffler
// interface.
type ints []int

func (s ints) Len() int      { return len(s) }
func (s ints) Swap(i, j int) { s[i], s[j] = s[j], s[i] }

// Example program.  Make an ints collection, fill with sequential numbers,
// print, shuffle, print.
func main() {
a := make(ints, 20)
for i := range a {
a[i] = i
}
fmt.Println(a)
shuffle(a)
fmt.Println(a)
}


{{out|Example output}} (of either program)


[0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19]
[11 10 12 19 4 13 15 17 14 2 5 18 8 0 6 9 7 3 1 16]



Groovy

Solution:

def shuffle = { list ->
if (list == null || list.empty) return list
def r = new Random()
def n = list.size()
(n..1).each { i ->
def j = r.nextInt(i)
list[[i-1, j]] = list[[j, i-1]]
}
list
}


Test:

def list = [] + (0..20)
println list
println shuffle(list)
println shuffle(list)
println shuffle(list)


{{out}}

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
[12, 16, 7, 13, 1, 9, 17, 20, 15, 3, 5, 6, 8, 0, 18, 10, 14, 4, 2, 11, 19]
[17, 6, 10, 1, 18, 5, 7, 13, 2, 11, 16, 3, 14, 0, 4, 20, 19, 12, 8, 9, 15]
[6, 20, 11, 4, 7, 12, 5, 14, 19, 18, 13, 15, 1, 2, 8, 16, 17, 10, 0, 9, 3]


import System.Random (randomRIO)

mkRands :: Int -> IO [Int]
mkRands = mapM (randomRIO . (,) 0) . enumFromTo 1 . pred

replaceAt :: Int -> a -> [a] -> [a]
replaceAt i c l =
let (a, b) = splitAt i l
in a ++ c : drop 1 b

swapElems :: (Int, Int) -> [a] -> [a]
swapElems (i, j) xs
| i == j = xs
| otherwise = replaceAt j (xs !! i) $replaceAt i (xs !! j) xs knuthShuffle :: [a] -> IO [a] knuthShuffle xs = (foldr swapElems xs . zip [1 ..]) <$> mkRands (length xs)


or, as an alternative to making two indexed references into the list with '''(!!)''':

import System.Random (randomRIO)
import Data.Bool (bool)

knuthShuffle :: [a] -> IO [a]
knuthShuffle xs = (foldr swapped xs . zip [1 ..]) <$> randoms (length xs) swapped :: (Int, Int) -> [a] -> [a] swapped (i, j) xs = let go (a, b) | a == b = xs | otherwise = let (m, n) = bool (b, a) (a, b) (b > a) (l, hi:t) = splitAt m xs (ys, lo:zs) = splitAt (pred (n - m)) t in concat [l, lo : ys, hi : zs] in bool xs (go (i, j))$ ((&&) . (i <) <*> (j <)) $length xs randoms :: Int -> IO [Int] randoms x = mapM (randomRIO . (,) 0) [1 .. pred x] main :: IO () main = knuthShuffle ['a' .. 'k'] >>= print  Examples of use of either of the two versions above: *Main> knuthShuffle ['a'..'k'] "bhjdgfciake" *Main> knuthShuffle$ map(ap (,)(+10)) [0..9]
[(0,10),(8,18),(2,12),(3,13),(9,19),(4,14),(7,17),(1,11),(6,16),(5,15)]


Function for showing intermediate results:

knuthShuffleProcess :: (Show a) => [a] -> IO ()
knuthShuffleProcess =
(mapM_ print. reverse =<<). ap (fmap. (. zip [1..]). scanr swapElems) (mkRands. length)


{{out}} Detailed example:

*Main> knuthShuffleProcess  ['a'..'k']
"abcdefghijk"
"abckefghijd"


An imperative implementation using arrays and the ST monad:

import Data.Array.ST
import Data.STRef
import Control.Arrow
import System.Random

shuffle :: RandomGen g => [a] -> g -> ([a], g)
shuffle list g = runST $do r <- newSTRef g let rand range = liftM (randomR range) (readSTRef r) >>= runKleisli (second (Kleisli$ writeSTRef r) >>> arr fst)
a <- newAry (1, len) list
forM_ [len, len - 1 .. 2] $\n -> do k <- rand (1, n) liftM2 (,) (readArray a k) (readArray a n) >>= runKleisli (Kleisli (writeArray a n) *** Kleisli (writeArray a k)) liftM2 (,) (getElems a) (readSTRef r) where len = length list newAry :: (Int, Int) -> [a] -> ST s (STArray s Int a) newAry = newListArray  =={{header|Icon}} and {{header|Unicon}}== The shuffle method used here can shuffle lists, record fields, and strings: procedure main() show(shuffle([3,1,4,1,5,9,2,6,3])) show(shuffle("this is a string")) end procedure shuffle(A) every A[i := *A to 1 by -1] :=: A[?i] return A end procedure show(A) every writes(!A," ") write() end  {{out}} ->ks 9 6 1 4 3 1 3 5 2 i n t i s r t g h s a i s ->  Note that the gloriously succinct 'standard' Icon shuffle: procedure shuffle(A) every !A :=: ?A end  is subtly biased. Inform 6 [ shuffle a n i j tmp; for(i = n - 1: i > 0: i--) { j = random(i + 1) - 1; tmp = a->j; a->j = a->i; a->i = tmp; } ];  J KS=:{~ (2&{.@[ {(|.@[)]} ])/@(,~(,.?@>:))@i.@#  The input array is transformed to a rectangular array of indexes. By doing this all kinds of arrays can serve as input (see examples below). The process is imitated by using using a fold, swapping elements in a restricted part of this index-array in each fold step. process J fold swap transform array <==> f / g y  Example of a transformed input: (,~(,.?@>:))@i.@# 1+i.6 0 0 0 0 0 0 1 1 0 0 0 0 2 0 0 0 0 0 3 2 0 0 0 0 4 3 0 0 0 0 5 0 0 0 0 0 0 1 2 3 4 5  The last row is the index-array that has to be shuffled. The other rows have valid indexes in the first two columns. The second column has a randomized value <= value first column. The index-swapping is done by the part: 2&{.@[ {(|.@[)]} ]  Finally, the shuffled indexes select elements from the original array. input { ~ shuffled indexes  Alternatively, instead of creating a rectangular array, the swapping indices and the original data can be individually boxed. In other words, (,~ (,. ?@>:))@i.@# can be replaced with |.@; ;&~./@(,. ?@>:)@i.@#, and the swapping can be achieved using (<@C. >)/ instead of (2&{.@[ {(|.@[)]} ])/. With this approach, the data structure with the swapping indices and the original data could look like this:  (|.@; ;&~./@(,. ?@>:)@i.@#)'abcde' +---+-+---+---+-+-----+ |4 2|3|2 1|1 0|0|abcde| +---+-+---+---+-+-----+  Note that we have the original data here, instead of indices to select all of its items. Note also that we have only a single value in a box where an item is being "swapped" with itself (this is required by J's cycle operation (C.)). The resulting definition looks like this:  (<@C. >)/@(|.@; ;&~./@(,. ?@>:)@i.@#)  Note that here we did not wind up with a list of indices which we used to permute the original data set. That data set is permuted directly. However, it is in a box and we do have to remove it from that box. Permuting the data directly, instead of permuting indices, has performance implications when the items being swapped are large, but see the note at the end of this entry for J for how you would do this operation in a "real" J program. Examples: ]A=: 5+i.9 5 6 7 8 9 10 11 12 13  Shuffle: KS A 13 10 7 5 11 9 8 6 12  Input ]M=: /:~(1 2 3,:2 3 4),(11 2 3,: 0 11 2),(1 1 1,:1 0),:1 1 1,:1 0 1 1 1 1 1 0 0 1 1 1 1 0 1 1 2 3 2 3 4 11 2 3 0 11 2  Shuffle KS M 11 2 3 0 11 2 1 1 1 1 0 1 1 1 1 1 0 0 1 2 3 2 3 4  Input ]L=:'aA';'bbB';'cC%$';'dD@'
+--+---+----+---+
|aA|bbB|cC%$|dD@| +--+---+----+---+  Shuffle KS L +--+----+---+---+ |aA|cC%$|dD@|bbB|
+--+----+---+---+


In J the shuffling of an arbitrary array can easily be implemented by the phrase ( ref http://www.jsoftware.com/jwiki/JPhrases/RandomNumbers ):

({~?~@#)


Applied on the former examples:

({~?~@#) A
8 7 13 6 10 11 5 9 12

({~?~@#) M
1  1 1
1  0 1

1  2 3
2  3 4

11  2 3
0 11 2

1  1 1
1  0 0

({~?~@#) L
+----+---+--+---+
|cC%$|bbB|aA|dD@| +----+---+--+---+  Java import java.util.Random; public static final Random gen = new Random(); // version for array of ints public static void shuffle (int[] array) { int n = array.length; while (n > 1) { int k = gen.nextInt(n--); //decrements after using the value int temp = array[n]; array[n] = array[k]; array[k] = temp; } } // version for array of references public static void shuffle (Object[] array) { int n = array.length; while (n > 1) { int k = gen.nextInt(n--); //decrements after using the value Object temp = array[n]; array[n] = array[k]; array[k] = temp; } }  JavaScript ES5 function knuthShuffle(arr) { var rand, temp, i; for (i = arr.length - 1; i > 0; i -= 1) { rand = Math.floor((i + 1) * Math.random());//get random between zero and i (inclusive) temp = arr[rand];//swap i and the zero-indexed number arr[rand] = arr[i]; arr[i] = temp; } return arr; } var res = { '1,2,3': 0, '1,3,2': 0, '2,1,3': 0, '2,3,1': 0, '3,1,2': 0, '3,2,1': 0 }; for (var i = 0; i < 100000; i++) { res[knuthShuffle([1,2,3]).join(',')] += 1; } for (var key in res) { print(key + "\t" + res[key]); }  Results in: 1,2,3 16619 1,3,2 16614 2,1,3 16752 2,3,1 16959 3,1,2 16460 3,2,1 16596  ES6 ====Mutating in-place swap==== (() => { // knuthShuffle :: [a] -> [a] const knuthShuffle = xs => enumFromTo(0, xs.length - 1) .reduceRight((a, i) => { const iRand = randomRInt(0, i), tmp = a[iRand]; return iRand !== i ? ( a[iRand] = a[i], a[i] = tmp, a ) : a; }, xs); const test = () => knuthShuffle( (alpha beta gamma delta epsilon zeta eta theta iota kappa lambda mu) .split(/\s+/) ); // GENERIC FUNCTIONS ---------------------------------- // enumFromTo :: Int -> Int -> [Int] const enumFromTo = (m, n) => n >= m ? ( iterateUntil(x => x >= n, x => 1 + x, m) ) : []; // iterateUntil :: (a -> Bool) -> (a -> a) -> a -> [a] const iterateUntil = (p, f, x) => { let vs = [x], h = x; while (!p(h))(h = f(h), vs.push(h)); return vs; }; // randomRInt :: Int -> Int -> Int const randomRInt = (low, high) => low + Math.floor( (Math.random() * ((high - low) + 1)) ); return test(); })();  {{Out}} e.g. ["iota", "epsilon", "kappa", "theta", "gamma", "delta", "lambda", "eta", "zeta", "beta", "mu", "alpha"]  ====Non-mutating swap==== (() => { // knuthShuffle :: [a] -> [a] const knuthShuffle = xs => enumFromTo(0, xs.length - 1) .reduceRight((a, i) => { const iRand = randomRInt(0, i); return i !== iRand ? ( swapped(i, iRand, a) ) : a; }, xs); const test = () => knuthShuffle( (alpha beta gamma delta epsilon zeta eta theta iota kappa lambda mu) .split(/\s+/) ); // Non mutating version of swapped // swapped :: Int -> Int -> [a] -> [a] const swapped = (iFrom, iTo, xs) => xs.map( (x, i) => iFrom !== i ? ( iTo !== i ? ( x ) : xs[iFrom] ) : xs[iTo] ); // GENERIC FUNCTIONS ---------------------------------- // enumFromTo :: Int -> Int -> [Int] const enumFromTo = (m, n) => n >= m ? ( iterateUntil(x => x >= n, x => 1 + x, m) ) : []; // iterateUntil :: (a -> Bool) -> (a -> a) -> a -> [a] const iterateUntil = (p, f, x) => { let vs = [x], h = x; while (!p(h))(h = f(h), vs.push(h)); return vs; }; // randomRInt :: Int -> Int -> Int const randomRInt = (low, high) => low + Math.floor( (Math.random() * ((high - low) + 1)) ); // zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] const zipWith = (f, xs, ys) => Array.from({ length: Math.min(xs.length, ys.length) }, (_, i) => f(xs[i], ys[i], i)); // MAIN --- return test(); })();  {{Out}} e.g. ["mu", "theta", "beta", "eta", "delta", "epsilon", "kappa", "alpha", "gamma", "lambda", "zeta", "iota"]  Joy DEFINE knuth-shuffle == (* Take the size of the array (without destroying it) *) dup dup size (* Generate a list of as many random numbers *) [rand] [rem] enconcat map (* Zip the two lists *) swap zip (* Sort according to the new index number *) [small] [] [uncons unswonsd [first >] split [swons] dip2] [enconcat] binrec (* Delete the new index number *) [second] map.  Using knuth-shuffle (file shuffle.joy): (* Sorted array of 21 integers *) [ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20] knuth-shuffle.  Command line: : joy shuffle.joy {{out}}  usrlib is loaded inilib is loaded agglib is loaded [12 6 8 4 14 18 7 15 1 0 11 13 5 10 16 2 19 17 9 20 3]  Julia {{works with|Julia|0.6}} function knuthshuffle!(r::AbstractRNG, v::AbstractVector) for i in length(v):-1:2 j = rand(r, 1:i) v[i], v[j] = v[j], v[i] end return v end knuthshuffle!(v::AbstractVector) = knuthshuffle!(Base.Random.GLOBAL_RNG, v) v = collect(1:20) println("# v =$v\n   -> ", knuthshuffle!(v))


{{out}}

# v = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
-> [16, 5, 17, 10, 2, 7, 20, 14, 4, 8, 19, 15, 18, 12, 11, 1, 9, 13, 3, 6]


Kotlin

object Knuth {
internal val gen = java.util.Random()
}

fun <T> Array<T>.shuffle(): Array<T> {
val a = clone()
var n = a.size
while (n > 1) {
val k = Knuth.gen.nextInt(n--)
val t = a[n]
a[n] = a[k]
a[k] = t
}
return a
}

fun main(args: Array<String>) {
val str = "abcdefghijklmnopqrstuvwxyz".toCharArray()
(1..10).forEach {
val s = str.toTypedArray().shuffle().toCharArray()
println(s)
require(s.toSortedSet() == str.toSortedSet())
}

val ia = arrayOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
(1..10).forEach {
val s = ia.shuffle()
println(s.distinct())
require(s.toSortedSet() == ia.toSet())
}
}


{{out}}

xdhsvtnumjgbywiqoapcelkrfz
pjnegbiyzuhsrclodftwkmaqvx
bkmqwhzregifyanvsltxjupodc
ewhxrlybnjqpvdsozaimkucgft
pdqgoaymbzefnjrwuvilsckxht
kcpagyuehjswdtvnzfrlbxqomi
iztsmaygkblephcjfnwvxurdoq
pltdyjwivsehckzfaxruqogmbn
nytfbpmjicgkaueoxwrhlsqvdz
epucijbvrhwyzdlsqftagxmkon
[7, 4, 5, 9, 2, 1, 3, 8, 10, 6]
[8, 10, 5, 4, 3, 6, 1, 2, 7, 9]
[7, 9, 2, 1, 10, 4, 6, 5, 8, 3]
[9, 6, 1, 8, 2, 5, 10, 3, 4, 7]
[7, 3, 6, 9, 10, 2, 5, 4, 1, 8]
[2, 9, 1, 7, 5, 10, 8, 4, 6, 3]
[4, 2, 7, 3, 8, 5, 6, 10, 1, 9]
[4, 8, 7, 6, 10, 5, 2, 1, 3, 9]
[6, 3, 9, 4, 5, 2, 10, 8, 1, 7]
[3, 6, 9, 2, 10, 8, 7, 5, 1, 4]


LabVIEW

{{works with|LabVIEW|8.0 Full Development System}}

[[File:Knuth_shuffle_panel.png|200px]] [[File:Knuth_shuffle_diagram.png|200px]]

Lasso

define staticarray->swap(p1::integer,p2::integer) => {
fail_if(
#p1 < 1 or #p2 < 1 or
#p1 > .size or #p2 > .size,
'invalid parameters'
)
#p1 == #p2
? return

local(tmp) = .get(#p2)
.get(#p2)  = .get(#p1)
.get(#p1)  = #tmp
}
define staticarray->knuthShuffle => {
loop(-from=.size, -to=2, -by=-1) => {
.swap(math_random(1, loop_count), loop_count)
}
}

(1 to 10)->asStaticArray->knuthShuffle&asString


{{out}}

staticarray(9, 5, 6, 1, 10, 8, 3, 4, 2, 7)


Liberty BASIC

'Declared the UpperBound to prevent confusion with lots of 9's floating around....
UpperBound = 9
Dim array(UpperBound)

For i = 0 To UpperBound
array(i) = Int(Rnd(1) * 10)
Print array(i)
Next i

For i = 0 To UpperBound
'set a random value because we will need to use the same value twice
randval = Int(Rnd(1) * (UpperBound - i))
temp1 = array(randval)
temp2 = array((UpperBound - i))
array(randval) = temp2
array((UpperBound - i)) = temp1
Next i

Print
For i = 0 To UpperBound
Print array(i)
Next i

to swap :i :j :a
localmake "t item :i :a
setitem :i :a item :j :a
setitem :j :a :t
end
to shuffle :a
for [i [count :a] 2] [swap 1 + random :i :i :a]
end

make "a {1 2 3 4 5 6 7 8 9 10}
shuffle :a
show :a


Lhogho does not have a setitem, and also does things more 'function'ally.

to slice :lst :start :finish
local "res
make "res []
for "i [:start :finish 1] [
make "j item :i :lst
make "res se :res :j
]
op :res
end

to setitem :n :lst :val
local "lhs
local "rhs
make "lhs slice :lst 1 :n-1
make "rhs slice :lst :n+1 count :lst
op (se :lhs :val :rhs)
end

to swap :i :j :a
local "t
make "t item :i :a
make "a setitem :i :a item :j :a
make "a setitem :j :a :t
op :a
end

to shuffle :a
for "i [count :a 2]
[
make "a swap 1 + random :i :i :a
]
op :a
end

make "a ( list 1 2 3 4 5 6 7 8 9 10 )
make "a shuffle :a
show :a


Lua

function table.shuffle(t)
for n = #t, 1, -1 do
local k = math.random(n)
t[n], t[k] = t[k], t[n]
end

return t
end

math.randomseed( os.time() )
a = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
table.shuffle(a)
for i,v in ipairs(a) do print(i,v) end


M2000 Interpreter


Dim Base 0, A(3)
For k=1 to 6 {
A(0):=10,20, 30
For i=len(A())-1 to 0 {
let j=random(0,i)
Swap a(i), a(j)
}
Print A()
}



M4

divert(-1)
define(randSeed',141592653)
define(rand_t',eval(randSeed^(randSeed>>13))')
define(random',
define(randSeed',eval((rand_t^(rand_t<<18))&0x7fffffff))randSeed')
define(for',
ifelse($#,0,$0'',
ifelse(eval($2<=$3),1,
pushdef($1',$2)$4'popdef($1')$0($1',incr($2),$3,$4')')')') define(set',define($1[$2]',$3')')
define(get',defn($1[$2])')
define(new',set($1,size,0)') define(deck', new($1)for(x',1,$2, set($1',x,x)')'set($1',size,$2)')
define(show',
for(x',1,get($1,size),get($1,x)'ifelse(x,get($1,size),',, ')')') define(swap',set($1,$2,get($1,$4))'set($1,$4,$3)')
define(shuffle',
define(s',get($1,size))'for(x',1,decr(s), swap($1,x,get($1,x),eval(x+random%(s-x+1)))')') divert deck(b',52) show(b') shuffle(b') show(b')  {{out}}  1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52 6, 22, 33, 51, 35, 45, 16, 32, 7, 34, 10, 44, 5, 38, 43, 25, 29, 9, 37, 20, 21, 48, 24, 46, 8, 26, 41, 47, 49, 36, 14, 31, 15, 39, 12, 17, 13, 1, 3, 4, 27, 11, 28, 2, 19, 30, 42, 50, 18, 52, 40, 23  Mathematica Usage of built-in function: RandomSample[{1, 2, 3, 4, 5, 6}]  Custom function: Shuffle[input_List /; Length[input] >= 1] := Module[{indices = {}, allindices = Range[Length[input]]}, Do[ AppendTo[indices, Complement[allindices, indices][[RandomInteger[{1, i}]]]]; , {i, Length[input], 1, -1} ]; input[[indices]] ]  Example: Shuffle[{1, 2, 3, 4, 5, 6}]  MATLAB Because this shuffle is done using rounds of operations on subsets of decreasing size, this is not an algorithm that can be vectorized using built-in MATLAB functions. So, we have to go old-school, no fancy MATLAB trickery. function list = knuthShuffle(list) for i = (numel(list):-1:2) j = floor(i*rand(1) + 1); %Generate random int between 1 and i %Swap element i with element j. list([j i]) = list([i j]); end end  There is an alternate way to do this that is not a true Knuth Shuffle, but operates with the same spirit. This alternate version produces the same output, saves some space, and can be implemented in-line without the need to encapsulate it in a function call like the Knuth Shuffle. function list = randSort(list) list = list( randperm(numel(list)) ); end  Maxima /* Maxima has an implementation of Knuth shuffle */ random_permutation([a, b, c]);  =={{header|Modula-3}}== MODULE Shuffle EXPORTS Main; IMPORT IO, Fmt, Random; VAR a := ARRAY [0..9] OF INTEGER {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; PROCEDURE Shuffle(VAR a: ARRAY OF INTEGER) = VAR temp: INTEGER; n: INTEGER := NUMBER(a); BEGIN WITH rand = NEW(Random.Default).init() DO WHILE n > 1 DO WITH k = rand.integer(0, n - 1) DO DEC(n); temp := a[n]; a[n] := a[k]; a[k] := temp; END; END; END; END Shuffle; BEGIN Shuffle(a); FOR i := FIRST(a) TO LAST(a) DO IO.Put(Fmt.Int(a[i]) & " "); END; IO.Put("\n"); END Shuffle.  {{out}}  martin@thinkpad:~$ ./shuffle
9 2 7 3 6 8 4 5 1 10
martin@thinkpad:~$./shuffle 1 7 8 10 5 4 6 3 9 2  MUMPS Shuffle(items,separator) New ii,item,list,n Set list="",n=0 Set ii="" For Set ii=$Order(items(ii)) Quit:ii=""  Do
. Set n=n+1,list(n)=items(ii),list=list_$Char(n) . Quit For Quit:list="" Do . Set n=$Random($Length(list))+1 . Set item=list($ASCII(list,n))
. Set $Extract(list,n)="" . Write item,separator . Quit Quit CardDeck New card,ii,suite Set ii=0 For suite="Spades","Hearts","Clubs","Diamonds" Do . For card=2:1:10,"Jack","Queen","King","Ace" Do . . Set ii=ii+1,items(ii)=card_" of "_suite . . Quit . Quit Quit Kill items Set items(91)="Red" Set items(82)="White" Set items(73)="Blue" Set items(64)="Yellow" Set items(55)="Green" Do Shuffle(.items," ") ; Red Yellow White Green Blue Do Shuffle(.items," ") ; Red Blue Yellow White Green Do Shuffle(.items," ") ; Green Blue Yellow White Red Kill items Do CardDeck,Shuffle(.items,$Char(13,10))
Queen of Hearts
9 of Diamonds
10 of Hearts
King of Hearts
7 of Diamonds
9 of Clubs
6 of Diamonds
8 of Diamonds
Ace of Hearts
Queen of Diamonds
9 of Hearts
2 of Hearts
King of Clubs
7 of Clubs
6 of Clubs
3 of Diamonds
Queen of Clubs
4 of Hearts
Ace of Diamonds
Ace of Clubs
10 of Diamonds
Jack of Diamonds
8 of Clubs
Jack of Hearts
10 of Clubs
4 of Diamonds
3 of Hearts
2 of Diamonds
5 of Hearts
Jack of Clubs
2 of Clubs
5 of Diamonds
6 of Hearts
4 of Clubs
3 of Clubs
7 of Hearts
8 of Hearts
King of Diamonds
5 of Clubs


Nemerle

Shuffle[T] (arr : array[T]) : array[T]
{
def rnd = Random();

foreach (i in [0 .. (arr.Length - 2)])
arr[i] <-> arr[(rnd.Next(i, arr.Length))];
arr
}


NetRexx

version 1

/* NetRexx */
options replace format comments java crossref savelog symbols nobinary

import java.util.List

cards = [String -
'hA', 'h2', 'h3', 'h4', 'h5', 'h6', 'h7', 'h8', 'h9', 'h10', 'hJ', 'hQ', 'hK' -
, 'cA', 'c2', 'c3', 'c4', 'c5', 'c6', 'c7', 'c8', 'c9', 'c10', 'cJ', 'cQ', 'cK' -
, 'dA', 'd2', 'd3', 'd4', 'd5', 'd6', 'd7', 'd8', 'd9', 'd10', 'dJ', 'dQ', 'dK' -
, 'sA', 's2', 's3', 's4', 's5', 's6', 's7', 's8', 's9', 's10', 'sJ', 'sQ', 'sK' -
]
cardsLen = cards.length
deck = ArrayList(cardsLen)
loop c_ = 0 to cardsLen - 1
end c_

showHand(deck)
deck = ArrayList shuffle(deck)
showHand(deck)

return

method shuffle(deck = List) public static binary returns List

rn = Random()
dl = deck.size

loop i_ = dl - 1 to 1 by -1
j_ = rn.nextInt(i_)
__ = deck.get(i_)
deck.set(i_, deck.get(j_))
deck.set(j_, __)
end i_

return deck

method showHand(deck = ArrayList) public static binary

dl = deck.size
hl = dl % 4
loop c_ = 0 to dl - 1 by hl
d_ = c_ + hl
if d_ >= dl then d_ = dl
say ArrayList(deck.subList(c_, d_)).toString
end c_
say

return


{{out}}


[hA, h2, h3, h4, h5, h6, h7, h8, h9, h10, hJ, hQ, hK]
[cA, c2, c3, c4, c5, c6, c7, c8, c9, c10, cJ, cQ, cK]
[dA, d2, d3, d4, d5, d6, d7, d8, d9, d10, dJ, dQ, dK]
[sA, s2, s3, s4, s5, s6, s7, s8, s9, s10, sJ, sQ, sK]

[s8, c10, sJ, c8, h10, h3, s3, d6, hJ, d3, c7, h5, s5]
[h8, d10, cK, s6, dQ, d9, d4, c4, c6, h6, cA, sA, dK]
[dJ, dA, d7, c2, d2, s10, sK, h2, c5, s7, cJ, d5, h9]
[c9, d8, c3, s9, cQ, sQ, h4, s4, hQ, h7, hK, hA, s2]



version 2

/* NetRexx ------------------------------------------------------------
* 08.01.2014 Walter Pachl modified to show state development a la Rexx
*--------------------------------------------------------------------*/
options replace format comments java crossref savelog symbols nobinary

import java.util.List

cards = [String '1','2','3','4','5','6','7','8','9','10']
cardsLen = cards.length
deck = ArrayList(cardsLen)
loop c_ = 0 to cardsLen - 1
end c_

showHand(deck,'In ')
deck = ArrayList shuffle(deck)
showHand(deck,'Out')
return

method shuffle(deck = List) public static binary returns List
rn = Random()
dl = deck.size
loop i_ = dl - 1 to 1 by -1
j_ = rn.nextInt(i_)
__ = deck.get(i_)
deck.set(i_, deck.get(j_))
deck.set(j_, __)
say i_ j_ ArrayList(deck.subList(0,i_+1)).toString
end i_
return deck

method showHand(deck = ArrayList,tag=REXX) public static binary
say tag ArrayList(deck.subList(0,deck.size)).toString
return


{{out}}

In  [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
9 5 [1, 2, 3, 4, 5, 10, 7, 8, 9, 6]
8 4 [1, 2, 3, 4, 9, 10, 7, 8, 5]
7 2 [1, 2, 8, 4, 9, 10, 7, 3]
6 0 [7, 2, 8, 4, 9, 10, 1]
5 4 [7, 2, 8, 4, 10, 9]
4 1 [7, 10, 8, 4, 2]
3 2 [7, 10, 4, 8]
2 0 [4, 10, 7]
1 0 [10, 4]
Out [10, 4, 7, 8, 2, 9, 1, 3, 5, 6]


Nim

import math
randomize()

proc shuffle[T](x: var seq[T]) =
for i in countdown(x.high, 0):
let j = random(i + 1)
swap(x[i], x[j])

var x = @[0,1,2,3,4,5,6,7,8,9]
shuffle(x)
echo x




@interface NSMutableArray (KnuthShuffle)
- (void)knuthShuffle;
@end
@implementation NSMutableArray (KnuthShuffle)
- (void)knuthShuffle {
for (NSUInteger i = self.count-1; i > 0; i--) {
NSUInteger j = arc4random_uniform(i+1);
[self exchangeObjectAtIndex:i withObjectAtIndex:j];
}
}
@end

int main() {
@autoreleasepool {
NSMutableArray *x = [NSMutableArray arrayWithObjects:@0, @1, @2, @3, @4, @5, @6, @7, @8, @9, nil];
[x knuthShuffle];
NSLog(@"%@", x);
}
return 0;
}


{{out}}


(
9,
4,
0,
8,
5,
3,
2,
1,
7,
6
)



OCaml

let shuffle arr =
for n = Array.length arr - 1 downto 1 do
let k = Random.int (n + 1) in
let temp = arr.(n) in
arr.(n) <- arr.(k);
arr.(k) <- temp
done


Oforth

Works with any object that has the property to be Indexable (Lists, Intervals, ...) Returns a new list

Indexable method: shuffle
| s i l |
self asListBuffer ->l
self size dup ->s 1- loop: i [ s i - rand i +  i  l swapValues ]
l dup freeze ;


Ol

There are two functions - one for tuples (that speedy) and second for lists (that uses previous one).

Ol is functional language, so we should make a copy of shuffling tuple and return this shuffled copy.


(define (shuffle tp)
(let ((items (vm:cast tp (type tp)))) ; make a copy
(for-each (lambda (i)
(let ((a (ref items i))
(j (+ 1 (rand! i))))
(set-ref! items i (ref items j))
(set-ref! items j a)))
(reverse (iota (size items) 1)))
items))

(define (list-shuffle tp)
(map (lambda (i)
(list-ref tp i))
(tuple->list
(shuffle (list->tuple (iota (length tp)))))))



Testing:


(define items (tuple 1 2 3 4 5 6 7 8 9))
(print "tuple before: " items)
(print "tuple after: " (shuffle items))

(define items (list 1 2 3 4 5 6 7 8 9))
(print "list before: " items)
(print "list after: " (list-shuffle items))



Output:


tuple before: #[1 2 3 4 5 6 7 8 9]
tuple after: #[9 4 1 3 7 2 5 6 8]
list before: (1 2 3 4 5 6 7 8 9)
list after: (8 2 4 9 5 3 6 1 7)



Oz

declare
proc {Shuffle Arr}
Low = {Array.low Arr}
High = {Array.high Arr}
in
for I in High..Low;~1 do
J = Low + {OS.rand} mod (I - Low + 1)
OldI = Arr.I
in
Arr.I := Arr.J
Arr.J := OldI
end
end

X = {Tuple.toArray unit(0 1 2 3 4 5 6 7 8 9)}
in
{Show {Array.toRecord unit X}}
{Shuffle X}
{Show {Array.toRecord unit X}}


PARI/GP

FY(v)={
forstep(n=#v,2,-1,
my(i=random(n)+1,t=v[i]);
v[i]=v[n];
v[n]=t
);
v
};

FY(vector(52,i,i))


Pascal

program Knuth;

const
startIdx = -5;
max = 11;
type
tmyData = string[9];
tmylist = array [startIdx..startIdx+max-1] of tmyData;

procedure InitList(var a: tmylist);
var
i: integer;
Begin
for i := Low(a) to High(a) do
str(i:3,a[i])
end;

procedure shuffleList(var a: tmylist);
var
i,k : integer;
tmp: tmyData;
begin
for i := High(a)-low(a) downto 1 do begin
k := random(i+1) + low(a);
tmp := a[i+low(a)]; a[i+low(a)] := a[k]; a[k] := tmp
end
end;

procedure DisplayList(const a: tmylist);
var
i : integer;
Begin
for i := Low(a) to High(a) do
write(a[i]);
writeln
end;

{ Test and display }
var
a: tmylist;
i: integer;
begin
randomize;
InitList(a);
DisplayList(a);
writeln;
For i := 0 to 4 do
Begin
shuffleList(a);
DisplayList(a);
end;
end.


{{out}}

 -5 -4 -3 -2 -1  0  1  2  3  4  5

-5  4  0 -4  3 -1 -3  1 -2  5  2
2  0  1 -5 -1  5 -3  4 -2  3 -4
3 -1 -2  5 -4  1  2 -5 -3  4  0
-4  1 -1 -5  5  2  0  3 -2 -3  4
-3 -5  4  2 -4  0  5  3  1 -1 -2


Perl

sub shuffle {
my @a = @_;
foreach my $n (1 ..$#a) {
my $k = int rand$n + 1;
$k ==$n or @a[$k,$n] = @a[$n,$k];
}
return @a;
}


Perl 6

{{works with|Rakudo|#21 "Seattle"}}

sub shuffle (@a is copy) {
for 1 ..^ @a -> $n { my$k = (0 .. $n).pick;$k == $n or @a[$k, $n] = @a[$n, $k]; } return @a; }  The shuffle is also built into the pick method on lists when you pass it a "whatever" for the number to pick: my @deck = @cards.pick(*);  Phix sequence cards = tagset(52) puts(1,"Before: ") ?cards for i=52 to 1 by -1 do integer r = rand(i) {cards[r],cards[i]} = {cards[i],cards[r]} end for puts(1,"After: ") ?cards puts(1,"Sorted: ") ?sort(cards)  {{out}} Before: {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52} After: {42,4,48,28,11,3,52,51,22,2,49,38,25,33,27,35,18,44,5,7,21,13,36,29,43,6,9,31,10,30,20,16,46,34,8,17,14,45,37,24,32,41,50,15,39,40,47,23,1,12,26,19} Sorted: {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52}  ## PHP php //The Fisher-Yates original Method function yates_shuffle($arr){
$shuffled = Array(); while($arr){
$rnd = array_rand($arr);
$shuffled[] =$arr[$rnd]; array_splice($arr, $rnd, 1); } return$shuffled;
}

//The modern Durstenfeld-Knuth algorithm
function knuth_shuffle(&$arr){ for($i=count($arr)-1;$i>0;$i--){$rnd = mt_rand(0,$i); list($arr[$i],$arr[$rnd]) = array($arr[$rnd],$arr[$i]); } }  ## PicoLisp PicoLisp (seed (in "/dev/urandom" (rd 8))) (de knuth (Lst) (for (N (length Lst) (>= N 2) (dec N)) (let I (rand 1 N) (xchg (nth Lst N) (nth Lst I)) ) ) ) (let L (range 1 15) (println 'before L) (knuth L) (println 'after L) )  {{out}} txt before (1 2 3 4 5 6 7 8 9 10 11 12 13 14 15) after (12 15 4 13 11 9 7 1 2 14 5 6 8 3 10)  ## PL/I ### version 1 pli declare T(0:10) fixed binary initial (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11); declare (i, j, temp) fixed binary; do i = lbound(T,1) to hbound(T,1); j = min(random() * 12, 11); temp = T(j); T(j) = T(i); T(i) = temp; end;  ### version 2 pli kn: Proc Options(main); /*-------------------------------------------------------------------- * 07.01.2014 Walter Pachl translated from REXX version 2 * Iteration i: only the first i elements are candidates for swapping *-------------------------------------------------------------------*/ Dcl T(10) Bin Fixed(15) Init(1,2,3,4,5,6,7,8,9,10); Dcl (i,j,temp) Bin Fixed(15) init(0); Dcl h Char(6); Call show('In',10); /* show start */ do i = 10 To 2 By -1; /* shuffle */ j=random()*i+1; Put string(h)Edit(i,j)(f(2),f(3)); temp=t(i); t(i)=t(j); t(j)=temp; /* t(i) <-> t(j) */ Call show(h,i); /* show intermediate states */ end; Call show('Out',10); /* show final state */ show: Proc(txt,n); Dcl txt Char(*); Dcl n Bin Fixed(15); Put Edit(txt,(t(k) do k=1 To n))(Skip,a(7),10(f(3))); End; end;  {{out}} txt In 1 2 3 4 5 6 7 8 9 10 10 5 1 2 3 4 10 6 7 8 9 5 9 1 9 2 3 4 10 6 7 8 1 8 7 9 2 3 4 10 6 8 7 7 2 9 8 3 4 10 6 2 6 6 9 8 3 4 10 6 5 3 9 8 10 4 3 4 2 9 4 10 8 3 3 9 4 10 2 1 4 9 Out 4 9 10 8 3 6 2 7 1 5  ## PowerShell {{works with|PowerShell|3}} powershell$A = 1, 2, 3, 4, 5
Get-Random $A -Count$A.Count


{{works with|PowerShell|2}}

powershell
function shuffle ($a) {$c = $a.Clone() # make copy to avoid clobbering$a
1..($c.Length - 1) | ForEach-Object {$i = Get-Random -Minimum $_ -Maximum$c.Length
$c[$_-1],$c[$i] = $c[$i],$c[$_-1]
$c[$_-1]  # return newly-shuffled value
}
$c[-1] # last value }  This yields the values one by one instead of returning the array as a whole, so the rest of the pipeline can work on the values while shuffling is still in progress. ## PureBasic PureBasic EnableExplicit Procedure KnuthShuffle(Array a(1)) Protected i, last = ArraySize(a()) For i = last To 1 Step -1 Swap a(i), a(Random(i)) Next EndProcedure Procedure.s ArrayToString(Array a(1)) Protected ret$, i, last = ArraySize(a())

ret$= Str(a(0)) For i = 1 To last ret$ + "," + Str(a(i))
Next
ProcedureReturn ret$EndProcedure #NumElements = 10 Dim a(#NumElements-1) Define i For i = 0 To #NumElements-1 a(i) = i Next KnuthShuffle(a()) Debug "shuffled: " + ArrayToString(a())  {{out}} txt shuffled: 1,8,6,0,5,9,2,4,7,3  ## Python Python's standard library function [http://docs.python.org/library/random.html#random.shuffle random.shuffle] uses this algorithm and so should normally be used. The function below is very similar: python from random import randrange def knuth_shuffle(x): for i in range(len(x)-1, 0, -1): j = randrange(i + 1) x[i], x[j] = x[j], x[i] x = list(range(10)) knuth_shuffle(x) print("shuffled:", x)  {{out}} txt shuffled: [5, 1, 6, 0, 8, 4, 2, 3, 9, 7]  We could also write our own Knuth shuffle function as a fold, with a non-mutating swap function: {{Works with|Python|3.7}} python '''Knuth shuffle as a fold''' from functools import reduce from random import randint # knuthShuffle :: [a] -> IO [a] def knuthShuffle(xs): '''A pseudo-random shuffle of the elements in xs.''' return reduce( swapped, enumerate(randoms(len(xs))), xs ) # swapped :: (Int, Int) -> [a] -> [a] def swapped(xs, ij): '''New list in which the elements at indices i and j of xs are swapped. ''' def go(a, b): if a != b: m, n = (a, b) if b > a else (b, a) l, ht = splitAt(m)(xs) ys, zs = splitAt((n - m) - 1)(ht[1:]) return l + [zs[0]] + ys + [ht[0]] + zs[1:] else: return xs i, j = ij z = len(xs) - 1 return xs if i > z or j > z else go(i, j) # randoms :: Int -> IO [Int] def randoms(n): '''Pseudo-random list of n - 1 indices. ''' return list(map(randomRInt(0)(n - 1), range(1, n))) # TEST ---------------------------------------------------- # main :: IO () def main(): '''Repeated Knuth shuffles of ['a' .. 'k']''' print( fTable(main.__doc__ + ':\n')(str)(lambda x: ''.join(x))( lambda _: knuthShuffle(list('abcdefghijk')) )(range(1, 11)) ) # GENERIC ------------------------------------------------- # randomRInt :: Int -> Int -> IO () -> Int def randomRInt(m): '''The return value of randomRInt is itself a function. The returned function, whenever called, yields a a new pseudo-random integer in the range [m..n]. ''' return lambda n: lambda _: randint(m, n) # splitAt :: Int -> [a] -> ([a], [a]) def splitAt(n): '''A tuple pairing the prefix of length n with the rest of xs. ''' return lambda xs: (xs[0:n], xs[n:]) # FORMATTING ----------------------------------------------------------- # fTable :: String -> (a -> String) -> # (b -> String) -> (a -> b) -> [a] -> String def fTable(s): '''Heading -> x display function -> fx display function -> f -> xs -> tabular string. ''' def go(xShow, fxShow, f, xs): ys = [xShow(x) for x in xs] w = max(map(len, ys)) return s + '\n' + '\n'.join(map( lambda x, y: y.rjust(w, ' ') + ' -> ' + fxShow(f(x)), xs, ys )) return lambda xShow: lambda fxShow: lambda f: lambda xs: go( xShow, fxShow, f, xs ) # MAIN --- if __name__ == '__main__': main()  {{Out}} txt Repeated Knuth shuffles of ['a' .. 'k']: 1 -> kdafbhigejc 2 -> jhdkgeicabf 3 -> aciebghdfkj 4 -> fjahegibckd 5 -> cabejfidkgh 6 -> gbecahfkijd 7 -> jegchkdifba 8 -> fcjkghiadeb 9 -> ihfebdajgkc 10 -> hjkigbadcfe  ## R See also, the built-in function 'sample'. Original Fisher-Yates version r fisheryatesshuffle <- function(n) { pool <- seq_len(n) a <- c() while(length(pool) > 0) { k <- sample.int(length(pool), 1) a <- c(a, pool[k]) pool <- pool[-k] } a }  Knuth variation: r fisheryatesknuthshuffle <- function(n) { a <- seq_len(n) while(n >=2) { k <- sample.int(n, 1) if(k != n) { temp <- a[k] a[k] <- a[n] a[n] <- temp } n <- n - 1 } a } #Example usage: fisheryatesshuffle(6) # e.g. 1 3 6 2 4 5 x <- c("foo", "bar", "baz", "quux") x[fisheryatesknuthshuffle(4)] # e.g. "bar" "baz" "quux" "foo"  ## Racket scheme #lang racket (define (swap! vec i j) (let ([tmp (vector-ref vec i)]) (vector-set! vec i (vector-ref vec j)) (vector-set! vec j tmp))) (define (knuth-shuffle x) (if (list? x) (vector->list (knuth-shuffle (list->vector x))) (begin (for ([i (in-range (sub1 (vector-length x)) 0 -1)]) (define r (random (+ i 1))) (swap! x i r)) x))) (knuth-shuffle '(1 2 3 4))  ## REBOL rebol REBOL [ Title: "Fisher-Yates" Purpose: {Fisher-Yates shuffling algorithm} ] fisher-yates: func [b [block!] /local n i j k] [ n: length? b: copy b i: n while [i > 1] [ if i <> j: random i [ error? set/any 'k pick b j change/only at b j pick b i change/only at b i get/any 'k ] i: i - 1 ] b ]  ## REXX ===version 0, card pips=== rexx /*REXX program shuffles a deck of playing cards (with jokers) using the Knuth shuffle.*/ rank= 'A 2 3 4 5 6 7 8 9 10 J Q K' /*pips of the various playing cards. */ suit= '♣♠♦♥' /*suit " " " " " */ parse arg seed . /*obtain optional argument from the CL.*/ if datatype(seed,'W') then call random ,,seed /*maybe use for RANDOM repeatability.*/ say '══════════════════ getting a new deck out of the box ···' @.1= 'highJoker' /*good decks have a color joker, and a */ @.2= 'lowJoker' /* ··· black & white joker. */ cards=2 /*now, there're 2 cards are in the deck*/ do j =1 for length(suit) do k=1 for words(rank); cards=cards + 1 @.cards=substr(suit, j, 1)word(rank, k) end /*k*/ end /*j*/ call show say; say '══════════════════ shuffling' cards "cards ···" do s=cards by -1 to 2; ?=random(1,s); parse value @.? @.s with @.s @.? /* [↑] swap two cards in the deck. */ end /*s*/ call show exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ show: _=; do m=1 for cards; _=_ @.m; end /*m*/; say _; return  '''output''' txt ══════════════════ getting a new deck out of the box ··· highJoker lowJoker ♣A ♣2 ♣3 ♣4 ♣5 ♣6 ♣7 ♣8 ♣9 ♣10 ♣J ♣Q ♣K ♠A ♠2 ♠3 ♠4 ♠5 ♠6 ♠7 ♠8 ♠9 ♠10 ♠J ♠Q ♠K ♦A ♦2 ♦3 ♦4 ♦5 ♦6 ♦7 ♦8 ♦9 ♦10 ♦J ♦Q ♦K ♥A ♥2 ♥3 ♥4 ♥5 ♥6 ♥7 ♥8 ♥9 ♥10 ♥J ♥Q ♥K ══════════════════ shuffling 54 cards ··· ♣J ♦3 ♥5 ♣10 ♥2 ♥J ♣6 ♦4 ♠2 ♥8 ♥A ♠A ♣9 ♣5 ♠7 ♦6 ♥6 ♠10 ♥9 ♦2 lowJoker ♥3 ♠5 ♠K ♣K ♣8 ♣Q ♠Q ♣2 ♦8 ♠4 ♣7 ♦5 ♥K ♣A ♠6 ♠J ♦Q ♦7 ♠9 ♦10 ♦K ♣4 ♥7 ♣3 ♠3 highJoker ♦A ♥4 ♦J ♠8 ♦9 ♥Q ♥10  ===version 1, card names=== This version handles items with (leading/trailing/embedded) blanks in them, so '''parse''' isn't an option for shuffling. rexx /*REXX program shuffles a deck of playing cards (with jokers) using the Knuth shuffle.*/ rank = 'ace deuce trey 4 5 6 7 8 9 10 jack queen king' /*use pip names for cards*/ suit = 'club spade diamond heart' /* " suit " " " */ say '══════════════════ getting a new deck out of the box ···' @.1= ' color joker' /*good decks have a color joker, and a */ @.2= ' b&w joker' /* ··· black & white joker. */ cards=2 /*now, there're 2 cards are in the deck*/ do j =1 for words(suit) do k=1 for words(rank); cards=cards+1 /*bump the card counter. */ @.cards=right(word(suit,j),7) word(rank,k) /*assign a card name. */ end /*k*/ end /*j*/ call show 'ace' /*inserts blank when an ACE is found.*/ say; say '══════════════════ shuffling' cards "cards ···" do s=cards by -1 to 2; ?=random(1,s); _=@.?; @.?=@.s; @.s=_ end /*s*/ /* [↑] swap two cards in the deck. */ call show exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ show: parse arg break; say /*get separator card, show blank line. */ do m=1 for cards /* [↓] traipse through the card deck. */ if pos(break,@.m)\==0 then say /*show a blank to read cards easier. */ say 'card' right(m, 2) '───►' @.m /*display a particular card from deck. */ end /*m*/ return  '''output''' ══════════════════ getting a new deck out of the box ··· card 1 ───► color joker card 2 ───► b&w joker card 3 ───► club ace card 4 ───► club deuce card 5 ───► club trey card 6 ───► club 4 card 7 ───► club 5 card 8 ───► club 6 card 9 ───► club 7 card 10 ───► club 8 card 11 ───► club 9 card 12 ───► club 10 card 13 ───► club jack card 14 ───► club queen card 15 ───► club king card 16 ───► spade ace card 17 ───► spade deuce card 18 ───► spade trey card 19 ───► spade 4 card 20 ───► spade 5 card 21 ───► spade 6 card 22 ───► spade 7 card 23 ───► spade 8 card 24 ───► spade 9 card 25 ───► spade 10 card 26 ───► spade jack card 27 ───► spade queen card 28 ───► spade king card 29 ───► diamond ace card 30 ───► diamond deuce card 31 ───► diamond trey card 32 ───► diamond 4 card 33 ───► diamond 5 card 34 ───► diamond 6 card 35 ───► diamond 7 card 36 ───► diamond 8 card 37 ───► diamond 9 card 38 ───► diamond 10 card 39 ───► diamond jack card 40 ───► diamond queen card 41 ───► diamond king card 42 ───► heart ace card 43 ───► heart deuce card 44 ───► heart trey card 45 ───► heart 4 card 46 ───► heart 5 card 47 ───► heart 6 card 48 ───► heart 7 card 49 ───► heart 8 card 50 ───► heart 9 card 51 ───► heart 10 card 52 ───► heart jack card 53 ───► heart queen card 54 ───► heart king ══════════════════ shuffling 54 cards ··· card 1 ───► spade ace card 2 ───► heart jack card 3 ───► heart ace card 4 ───► diamond 10 card 5 ───► spade 7 card 6 ───► club 10 card 7 ───► club trey card 8 ───► diamond deuce card 9 ───► diamond 7 card 10 ───► spade queen card 11 ───► heart queen card 12 ───► spade deuce card 13 ───► spade 9 card 14 ───► diamond 4 card 15 ───► diamond ace card 16 ───► heart 6 card 17 ───► club king card 18 ───► color joker card 19 ───► spade 6 card 20 ───► heart 5 card 21 ───► diamond 8 card 22 ───► heart 8 card 23 ───► club 7 card 24 ───► heart king card 25 ───► club jack card 26 ───► diamond jack card 27 ───► heart 9 card 28 ───► spade trey card 29 ───► spade jack card 30 ───► spade king card 31 ───► heart 10 card 32 ───► diamond king card 33 ───► diamond trey card 34 ───► heart deuce card 35 ───► heart 4 card 36 ───► diamond 5 card 37 ───► diamond 9 card 38 ───► spade 4 card 39 ───► club 4 card 40 ───► club 5 card 41 ───► spade 5 card 42 ───► club 9 card 43 ───► b&w joker card 44 ───► club 6 card 45 ───► heart 7 card 46 ───► spade 8 card 47 ───► diamond 6 card 48 ───► club deuce card 49 ───► diamond queen card 50 ───► club queen card 51 ───► club ace card 52 ───► heart trey card 53 ───► spade 10 card 54 ───► club 8  ### version 2 rexx /* REXX --------------------------------------------------------------- * 05.01.2014 Walter Pachl * borrow one improvement from version 1 * 06.01.2014 removed -"- (many tests cost more than few "swaps") *--------------------------------------------------------------------*/ Call random ,,123456 /* seed for random */ Do i=1 To 10; a.i=i; End; /* fill array */ Call show 'In',10 /* show start */ do i = 10 To 2 By -1 /* shuffle */ j=random(i-1)+1; h=right(i,2) right(j,2) Parse Value a.i a.j With a.j a.i /* a.i <-> a.j */ Call show h,i /* show intermediate states */ end; Call show 'Out',10 /* show fomaö state */ Exit show: Procedure Expose a. Parse Arg txt,n ol=left(txt,6); Do k=1 To n; ol=ol right(a.k,2); End Say ol Return  {{out}} txt In 1 2 3 4 5 6 7 8 9 10 10 2 1 10 3 4 5 6 7 8 9 2 9 6 1 10 3 4 5 9 7 8 6 8 6 1 10 3 4 5 8 7 9 7 3 1 10 7 4 5 8 3 6 5 1 10 7 4 8 5 5 1 8 10 7 4 1 4 1 4 10 7 8 3 1 7 10 4 2 1 10 7 Out 10 7 4 8 1 5 3 9 6 2  ## Ring ring # Project : Knuth shuffle items = list(52) for n = 1 to len(items) items[n] = n next knuth(items) showarray(items) func knuth(items) for i = len(items) to 1 step -1 j = random(i-1) + 1 if i != j temp = items[i] items[i] = items[j] items[j] = temp ok next func showarray(vect) see "[" svect = "" for n = 1 to len(vect) svect = svect + vect[n] + " " next svect = left(svect, len(svect) - 1) see svect see "]" + nl  txt [15 1 51 20 45 29 43 8 13 3 41 35 11 7 37 9 38 17 32 48 40 25 44 18 14 50 42 34 2 21 12 4 26 19 23 24 28 46 36 10 5 16 6 49 22 33 39 47 31 52 30 27]  ## Ruby {{trans|Tcl}} ruby class Array def knuth_shuffle! j = length i = 0 while j > 1 r = i + rand(j) self[i], self[r] = self[r], self[i] i += 1 j -= 1 end self end end r = Hash.new(0) 100_000.times do |i| a = [1,2,3].knuth_shuffle! r[a] += 1 end r.keys.sort.each {|a| puts "#{a.inspect} => #{r[a]}"}  results in txt [1, 2, 3] => 16572 [1, 3, 2] => 16610 [2, 1, 3] => 16633 [2, 3, 1] => 16714 [3, 1, 2] => 16838 [3, 2, 1] => 16633  '''More idomatic:''' ruby class Array def knuth_shuffle! (length - 1).downto(1) do |i| j = rand(i + 1) self[i], self[j] = self[j], self[i] end self end end  ## Run BASIC runbasic dim cards(52) for i = 1 to 52 ' make deck cards(i) = i next for i = 52 to 1 step -1 ' shuffle deck r = int((rnd(1)*i) + 1) if r <> i then hold = cards(r) cards(r) = cards(i) cards(i) = hold end if next print "== Shuffled Cards ==" ' print shuffled cards for i = 1 to 52 print cards(i);" "; if i mod 18 = 0 then print next print  ## Rust {{libheader|rand}} rust use rand::Rng; extern crate rand; fn knuth_shuffle(v: &mut [T]) { let mut rng = rand::thread_rng(); let l = v.len(); for n in 0..l { let i = rng.gen_range(0, l - n); v.swap(i, l - n - 1); } } fn main() { let mut v: Vec<_> = (0..10).collect(); println!("before: {:?}", v); knuth_shuffle(&mut v); println!("after: {:?}", v); }  ## Scala Scala def shuffle[T](a: Array[T]) = { for (i <- 1 until a.size reverse) { val j = util.Random nextInt (i + 1) val t = a(i) a(i) = a(j) a(j) = t } a }  ## Scheme A functional version, using lists (inefficient), somewhat unusual in reversing the entire initial sublist on each pass instead of just swapping: Scheme #!r6rs (import (rnrs base (6)) (srfi :27 random-bits)) (define (semireverse li n) (define (continue front back n) (cond ((null? back) front) ((zero? n) (cons (car back) (append front (cdr back)))) (else (continue (cons (car back) front) (cdr back) (- n 1))))) (continue '() li n)) (define (shuffle li) (if (null? li) () (let ((li-prime (semireverse li (random-integer (length li))))) (cons (car li-prime) (shuffle (cdr li-prime))))))  A mutable version, using vectors (efficient): Scheme #!r6rs (import (rnrs base (6)) (srfi :27 random-bits)) (define (vector-swap! vec i j) (let ((temp (vector-ref vec i))) (vector-set! vec i (vector-ref vec j)) (vector-set! vec j temp))) (define (countdown n) (if (zero? n) () (cons n (countdown (- n 1))))) (define (vector-shuffle! vec) (for-each (lambda (i) (let ((j (random-integer i))) (vector-swap! vec (- i 1) j))) (countdown (vector-length vec))))  ## Scratch See Knuth's shuffle in action. Visit [https://scratch.mit.edu/projects/65352234/ this Scratch implementation] to see a demo and inspect its source. ## Seed7 seed7$ include "seed7_05.s7i";

const type: intArray is array integer;

const proc: shuffle (inout intArray: a) is func
local
var integer: i is 0;
var integer: k is 0;
var integer: tmp is 0;
begin
for i range maxIdx(a) downto 2 do
k := rand(1, i);
tmp := a[i];
a[i] := a[k];
a[k] := tmp;
end for;
end func;

const proc: main is func
local
var intArray: a is 10 times 0;
var integer: i is 0;
begin
for key i range a do
a[i] := i;
end for;
shuffle(a);
for i range a do
write(i <& " ");
end for;
writeln;
end func;


{{out}}

txt

7 5 6 8 3 10 9 4 2 1



## Sidef

ruby
func knuth_shuffle(a) {
for i (a.len ^.. 1) {
var j = i.irand
a[i, j] = a[j, i]
}
return a
}

say knuth_shuffle(@(1..10))


{{out}}

txt

[7, 4, 3, 8, 9, 6, 10, 2, 1, 5]



## Smalltalk

{{works with|GNU Smalltalk}}

smalltalk
"The selector swap:with: is documented, but it seems not
implemented (GNU Smalltalk version 3.0.4); so here it is an implementation"
SequenceableCollection extend [
swap: i with: j [
|t|
t := self at: i.
self at: i put: (self at: j).
self at: j put: t.
]
].

Object subclass: Shuffler [
Shuffler class >> Knuth: aSequenceableCollection [
|n k|
n := aSequenceableCollection size.
[ n > 1 ] whileTrue: [
k := Random between: 1 and: n.
aSequenceableCollection swap: n with: k.
n := n - 1
]
]
].


Testing

smalltalk
"Test"
|c|
c := OrderedCollection new.
c addAll: #( 1 2 3 4 5 6 7 8 9 ).
Shuffler Knuth: c.
c display.


## SNOBOL4

SNOBOL4
* Library for random()
-include 'Random.sno'

*       # String -> array
define('s2a(str,n)i') :(s2a_end)
s2a     s2a = array(n); str = str ' '
sa1     str break(' ') . s2a span(' ') = :s(sa1)f(return)
s2a_end

*       # Array -> string
define('a2s(a)i') :(a2s_end)
a2s     a2s = a2s a ' ' :s(a2s)f(return)
a2s_end

*       # Knuth shuffle in-place
define('shuffle(a)alen,n,k,tmp') :(shuffle_end)
shuffle n = alen = prototype(a);
sh1     k = convert(random() * alen,'integer') + 1
eq(a,a) :s(sh2)
tmp = a; a = a; a = tmp
sh2     n = gt(n,1) n - 1 :s(sh1)
shuffle = a :(return)
shuffle_end

*       # Test and display
a = s2a('1 2 3 4 5 6 7 8 9 10',10)
output = a2s(a) '->'
shuffle(a)
output = a2s(a)
end


{{out}}

txt
1 2 3 4 5 6 7 8 9 10 ->
2 10 4 9 1 5 6 8 7 3


## Stata

stata
mata
function shuffle(a) {
n = length(a)
r = runiformint(1,1,1,1..n)
for (i=n; i>=2; i--) {
j = r[i]
x = a[i]
a[i] = a[j]
a[j] = x
}
return(a)
}

shuffle(1..10)
end


'''Output'''

txt
1    2    3    4    5    6    7    8    9   10
+---------------------------------------------------+
1 |   8   10    9    1    7    2    6    4    3    5  |
+---------------------------------------------------+


## Swift

'''Simple version (any Swift version):''' Extend Array with shuffle methods; using arc4random_uniform from C stdlib:

swift
import func Darwin.arc4random_uniform

extension Array {

func shuffle() -> Array {

var result = self; result.shuffleInPlace(); return result
}

mutating func shuffleInPlace() {

for i in 1 ..< count { swap(&self[i], &self[Int(arc4random_uniform(UInt32(i+1)))]) }
}

}

// Swift 2.0:
print([1, 2, 3, 4, 5, 6, 7, 8, 9, 10].shuffle())
// Swift 1.x:
//println([1, 2, 3, 4, 5, 6, 7, 8, 9, 10].shuffle())


{{out}}

txt
[8, 7, 2, 1, 6, 10, 5, 3, 4, 9]


'''Generic version (any Swift version):''' While the above code is generic in that it works with arrays of any element type, we can use generic global functions to define shuffling for any mutable collection with random-access index type which is far more generic than the above code:

swift
import func Darwin.arc4random_uniform

func shuffleInPlace(inout collection: T) {

let i0 = collection.startIndex

for i in i0.successor() ..< collection.endIndex {

arc4random_uniform(numericCast(
i0.distanceTo()
)+1)
))

swap(&collection[i], &collection[j])
}
}

func shuffle(collection: T) -> T {

var result = collection

shuffleInPlace(&result)

return result
}

// Swift 2.0:
print(shuffle([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]))
// Swift 1.x:
//println(shuffle([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]))


{{out}}

txt
[2, 5, 7, 1, 6, 10, 4, 3, 8, 9]


{{works with|Swift | 2.0 }} While the above solutions work with Swift 2.0 as they are, we can use Swift 2.0's Protocol Oriented Programming features to add shuffling methods to any mutable collection that has a random-access index:

swift
import func Darwin.arc4random_uniform

// Define a protocol for shuffling:

protocol Shufflable {

@warn_unused_result (mutable_variant="shuffleInPlace")
func shuffle() -> Self

mutating func shuffleInPlace()

}

// Provide a generalized implementation of the shuffling protocol for any mutable collection with random-access index:

extension Shufflable where Self: MutableCollectionType, Self.Index: RandomAccessIndexType {

func shuffle() -> Self {

var result = self

result.shuffleInPlace()

return result
}

mutating func shuffleInPlace() {

let i0 = startIndex

for i in i0+1 ..< endIndex {

arc4random_uniform(numericCast(
i0.distanceTo(i)
)+1)
))

swap(&self[i], &self[j])
}
}

}

// Declare Array's conformance to Shufflable:

extension Array: Shufflable
{ /* Implementation provided by Shufflable protocol extension */ }

print([1, 2, 3, 4, 5, 6, 7, 8, 9, 10].shuffle())


{{out}}

txt
[3, 1, 5, 6, 7, 8, 10, 2, 4, 9]


## Tcl

tcl
proc knuth_shuffle lst {
set j [llength $lst] for {set i 0} {$j > 1} {incr i;incr j -1} {
set r [expr {$i+int(rand()*$j)}]
set t [lindex $lst$i]
lset lst $i [lindex$lst $r] lset lst$r $t } return$lst
}

% knuth_shuffle {1 2 3 4 5}
2 1 3 5 4
% knuth_shuffle {1 2 3 4 5}
5 2 1 4 3
% knuth_shuffle {tom dick harry peter paul mary}
tom paul mary harry peter dick


As a test of skewing (an indicator of a poor implementation) this code was used:

tcl
% for {set i 0} {$i<100000} {incr i} { foreach val [knuth_shuffle {1 2 3 4 5}] pos {pos0 pos1 pos2 pos3 pos4} { incr tots($pos) $val } } % parray tots tots(pos0) = 300006 tots(pos1) = 300223 tots(pos2) = 299701 tots(pos3) = 299830 tots(pos4) = 300240  =={{header|TI-83 BASIC}}== Input L1, output L2. :"SHUFFLE" :L1→L2 :dim(L2)→A :For(B,1,dim(L2)-1) :randInt(1,A)→C :L2(C)→D :L2(A)→L2(C) :D→L2(A) :A-1→A :End :DelVar A :DelVar B :DelVar C :DelVar D :Return ## TUSCRIPT tuscript$$MODE TUSCRIPT oldnumbers=newnumbers="",range=20 LOOP nr=1,#range oldnumbers=APPEND(oldnumbers,nr) ENDLOOP PRINT "before ",oldnumbers LOOP r=#range,1,-1 RANDNR=RANDOM_NUMBERS (1,#r,1) shuffle=SELECT (oldnumbers,#randnr,oldnumbers) newnumbers=APPEND(newnumbers,shuffle) ENDLOOP PRINT "after ",newnumbers  {{out}} txt before 1'2'3'4'5'6'7'8'9'10'11'12'13'14'15'16'17'18'19'20 after 7'16'13'11'1'9'15'4'18'14'3'12'17'8'19'20'6'5'2'10  ## uBasic/4tH PRINT "before:" FOR L = 0 TO 51 @(L) = L PRINT @(L); " "; NEXT FOR L = 51 TO 0 STEP -1 C = RND(L + 1) IF C # L THEN PUSH @(C), L, @(L), C GOSUB 100 ENDIF NEXT PRINT : PRINT "after:" FOR L = 0 TO 51 PRINT @(L); " "; NEXT PRINT END 100 @(POP()) = POP() : @(POP()) = POP() : RETURN  {{out}} txt before: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 after: 19 4 49 9 27 35 50 11 2 29 22 48 33 15 17 42 47 28 41 18 34 21 30 39 3 8 23 12 36 26 0 46 7 44 13 14 16 40 10 25 31 32 51 24 20 38 45 6 43 1 5 37  ## UNIX Shell {{works with|ksh93}} {{works with|pdksh}} bash # Shuffle array[@]. function shuffle { integer i j t ((i =${#array[@]}))
while ((i > 1)); do
((j = RANDOM))                 # 0 <= j < 32768
((j < 32768 % i)) && continue  # no modulo bias
((j %= i))                     # 0 <= j < i

((i -= 1))
((t = array[i]))
((array[i] = array[j]))
((array[j] = t))
done
}

# Test program.
set -A array 11 22 33 44 55 66 77 88 99 110
shuffle
echo "\${array[@]}"


## Ursala

This function works on lists of any type and length, including character strings.

Ursala
shuffle = @iNX ~&l->r ^jrX/~&l ~&lK8PrC


test program:

Ursala
#cast %s

example = shuffle 'abcdefghijkl'


{{out}}

txt
'keacfjlbdigh'


## VBA

vb
Private Sub Knuth(Optional ByRef a As Variant)
Dim t As Variant, i As Integer
If Not IsMissing(a) Then
For i = UBound(a) To LBound(a) + 1 Step -1
j = Int((UBound(a) - LBound(a) + 1) * Rnd + LBound(a))
t = a(i)
a(i) = a(j)
a(j) = t
Next i
End If
End Sub
Public Sub program()
Dim b As Variant, c As Variant, d As Variant, e As Variant
Randomize
'imagine an empty array on this line
b = [{10}]
c = [{10, 20}]
d = [{10, 20, 30}]
e = [{11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22}]
f = [{"This ", "is ", "a ", "test"}]
Debug.Print "Before:"
Knuth 'feeding an empty array ;)
Debug.Print "After: "
Debug.Print "Before:";
For Each i In b: Debug.Print i;: Next i: Debug.Print
Knuth b
Debug.Print "After: ";
For Each i In b: Debug.Print i;: Next i: Debug.Print
Debug.Print "Before:";
For Each i In c: Debug.Print i;: Next i: Debug.Print
Knuth c
Debug.Print "After: ";
For Each i In c: Debug.Print i;: Next i: Debug.Print
Debug.Print "Before:";
For Each i In d: Debug.Print i;: Next i: Debug.Print
Knuth d
Debug.Print "After: ";
For Each i In d: Debug.Print i;: Next i: Debug.Print
Debug.Print "Before:";
For Each i In e: Debug.Print i;: Next i: Debug.Print
Knuth e
Debug.Print "After: ";
For Each i In e: Debug.Print i;: Next i: Debug.Print
Debug.Print "Before:";
For Each i In f: Debug.Print i;: Next i: Debug.Print
Knuth f
Debug.Print "After: ";
For Each i In f: Debug.Print i;: Next i: Debug.Print
End Sub

{{out}}
txt
Before:
After:
Before: 10
After:  10
Before: 10  20
After:  10  20
Before: 10  20  30
After:  20  10  30
Before: 11  12  13  14  15  16  17  18  19  20  21  22
After:  22  12  15  20  19  11  13  21  16  17  14  18
Before:This is a test
After: a This testis



## VBScript

;Implementation

vb

function shuffle( a )
dim i
dim r
randomize timer
for i = lbound( a ) to ubound( a )
r = int( rnd * ( ubound( a ) + 1 )  )
if r <> i then
swap a(i), a(r)
end if
next
shuffle = a
end function

sub swap( byref a, byref b )
dim tmp
tmp = a
a = b
b = tmp
end sub


;Invocation

vb
dim a
a = array( 1,2,3,4,5,6,7,8,9)
wscript.echo "before: ", join( a, ", " )
shuffle a
wscript.echo "after: ", join( a, ", " )
shuffle a
wscript.echo "after: ", join( a, ", " )
wscript.echo "--"
a = array( now(), "cow", 123, true, sin(1), 16.4 )
wscript.echo "before: ", join( a, ", " )
shuffle a
wscript.echo "after: ", join( a, ", " )
shuffle a
wscript.echo "after: ", join( a, ", " )


{{out}}

txt

before:  1, 2, 3, 4, 5, 6, 7, 8, 9
after:  6, 4, 1, 2, 7, 3, 5, 8, 9
after:  8, 7, 3, 2, 6, 5, 9, 1, 4
--
before:  16/02/2010 5:46:58 PM, cow, 123, True, 0.841470984807897, 16.4
after:  True, 16.4, 16/02/2010 5:46:58 PM, 123, cow, 0.841470984807897
after:  16.4, 16/02/2010 5:46:58 PM, 123, 0.841470984807897, True, cow



## Vedit macro language

The shuffle routine in [[Playing Cards]] shuffles text lines in edit buffer.
This example shuffles numeric registers #0 to #19.

The output will be inserted in current edit buffer.

vedit
// Test main
#90 = Time_Tick                   // seed for random number generator
#99 = 20                          // number of items in the array

IT("Before:") IN
for (#100 = 0; #100 < #99; #100++) {
#@100 = #100
Num_Ins(#@100, LEFT+NOCR) IT(" ")
}
IN

Call("SHUFFLE_NUMBERS")

IT("After:") IN
for (#100 = 0; #100 < #99; #100++) {
Num_Ins(#@100, LEFT+NOCR) IT(" ")
}
IN
Return

//--------------------------------------------------------------
// Shuffle numeric registers #0 to #nn
//  #99 = number of registers to shuffle (nn-1)
//
:SHUFFLE_NUMBERS:
for (#91 = #99-1; #91 > 0; #91--) {
Call("RANDOM")
#101 = Return_Value
#102 = #@101; #@101 = #@91; #@91 = #102
}
Return

//--------------------------------------------------------------
// Generate random numbers in range 0 <= Return_Value < #91
//  #90 = Seed    (0 to 0x7fffffff)
//  #91 = Scaling (0 to 0x10000)
//
:RANDOM:
#92 = 0x7fffffff / 48271
#93 = 0x7fffffff % 48271
#90 = (48271 * (#90 % #92) - #93 * (#90 / #92)) & 0x7fffffff
Return ((#90 & 0xffff) * #91 / 0x10000)


{{out}}

txt
Before:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
After:
9 13 8 18 10 1 17 15 0 16 14 19 3 2 7 11 6 4 5 12


## zkl

Two versions, imperative and functional, same results.
xs has to be a mutable list.

zkl
fcn kshuffle(xs){
foreach i in ([xs.len()-1..1,-1]){ xs.swap(i,(0).random(0,i+1)) }
xs
}
fcn kshufflep(xs){
[xs.len()-1..1,-1].pump(Void,'wrap(i){ xs.swap(i,(0).random(0,i+1)) })
xs
}


txt

var ns=(1).pump(10,List).copy() // [1..10] made mutable
kshuffle(ns)  //-->L(6,3,8,2,4,5,10,9,1,7)

ns="this is a test foo bar hoho".split(" ").copy();
kshufflep(ns)  //-->L("a","bar","hoho","foo","test","is","this")



`