Task
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'' ''j'' ''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
* 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
BR R14 return to caller
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
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)
(random$ m 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
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
e.g.
{"mu", "theta", "alpha", "delta", "zeta", "gamma",
"iota", "kappa", "lambda", "epsilon", "beta", "eta"}
ARM Assembly
/* 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
Dim $a[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] = $tmp
Next
EndFunc
array before permutation:
43 57 37 20 97 98 69 76 97 70
array after permutation:
57 69 97 70 37 97 20 76 43 98
AWK
Many [[Arrays#AWK|arrays in AWK]] have the first index at 1. This example shows how to shuffle such arrays. The elements can be integers, floating-point numbers, or strings.
# Shuffle an _array_ with indexes from 1 to _len_.
function shuffle(array, len, i, j, t) {
for (i = len; i > 1; i--) {
# j = random integer from 1 to i
j = int(i * rand()) + 1
# swap array[i], array[j]
t = array[i]
array[i] = array[j]
array[j] = t
}
}
# Test program.
BEGIN {
len = split("11 22 33 44 55 66 77 88 99 110", array)
shuffle(array, len)
for (i = 1; i < len; i++) printf "%s ", array[i]
printf "%s\n", array[len]
}
BASIC
RANDOMIZE TIMER
DIM cards(51) AS INTEGER
DIM L0 AS LONG, card AS LONG
PRINT "before:"
FOR L0 = 0 TO 51
cards(L0) = L0
PRINT LTRIM$(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$(cards(L0))); " ";
NEXT
PRINT
before:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
after:
27 14 37 35 3 44 25 38 46 1 22 49 2 51 16 32 20 30 4 33 36 6 31 21 41 34 9 13 0
50 47 48 40 39 7 18 19 26 24 10 29 5 12 28 11 17 43 45 8 23 42 15
=
Applesoft BASIC
=
As mentioned in the Sinclair ZX81 BASIC solution, for very small positive integer values, a string is a much more memory-efficient array, but here is an example of an array with numbers. Line 150 initializes and prints each element in the array. Line 190 performs the swap of the elements.
100 :
110 REM KNUTH SHUFFLE
120 :
130 DIM A(25)
140 FOR I = 1 TO 25
150 A(I) = I: PRINT A(I);" ";: NEXT I
160 PRINT : PRINT
170 FOR I = 25 TO 2 STEP - 1
180 J = INT ( RND (1) * I + 1)
190 T = A(I):A(I) = A(J):A(J) = T: NEXT I
200 FOR I = 1 TO 25
210 PRINT A(I);" ";: NEXT I
220 END
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
7 18 19 20 21 22 23 24 25
When it has finished, the screen will show (for example):
20 5 6 9 15 23 22 8 4 24 7 11 16 21 2 17
14 10 19 13 12 18 1 3 25
=
Sinclair ZX81 BASIC
=
For very small positive integer values, a string (which can be treated as an array of bytes) is much more memory-efficient than an array of numbers. In this program we shuffle a string consisting of the letters 'A' to 'Z'. The ZX81 is slow enough that we can watch the shuffle happening in real time, with items switching to inverse video display as they are shuffled. (This can be done, in the ZX81 character set, by setting the high bit in the character code.) Line 10 seeds the pseudo-random number generator. Note that strings (and arrays) are indexed from 1.
The program works with the unexpanded (1k RAM) ZX81.
10 RAND
20 LET A$=""
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
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.
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
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).
LINKAGE SECTION.
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
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}"
> 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;
}
[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 >
```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())
}
7,3,6,8,4,9,0,1,2,5
Elixir
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)
[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]}.
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
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
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
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
iArray.add(iCount)
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)
[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]
Haskell
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"
"jbckefghiad"
"jbckeighfad"
"jbckeihgfad"
"jbhkeicgfad"
"jbhiekcgfad"
"jbeihkcgfad"
"ibejhkcgfad"
"iebjhkcgfad"
"iebjhkcgfad"
An imperative implementation using arrays and the ST monad:
import Data.Array.ST
import Data.STRef
import Control.Monad
import Control.Monad.ST
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
->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();
})();
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();
})();
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
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
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))
# 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())
}
}
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
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
Logo
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')
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.
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
Jack of Spades
Ace of Hearts
Queen of Diamonds
9 of Hearts
2 of Hearts
King of Clubs
10 of Spades
7 of Clubs
6 of Clubs
3 of Diamonds
3 of Spades
Queen of Clubs
Ace of Spades
4 of Hearts
Ace of Diamonds
7 of Spades
Ace of Clubs
King of Spades
10 of Diamonds
Jack of Diamonds
8 of Clubs
4 of Spades
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
9 of Spades
3 of Clubs
5 of Spades
6 of Spades
7 of Hearts
8 of Spades
8 of Hearts
2 of Spades
Queen of Spades
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
deck.add(String(cards[c_]))
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
[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
deck.add(String(cards[c_]))
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
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
=={{header|Objective-C}}==
@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;
}
(
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.
-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
sub shuffle (@a is copy) {
for 1 ..^ @a -> $n {
my $k = (0 .. $n).pick;
$k == $n or @a[$k, $n] = @a[$n, $k];
}
return @a;
}
The shuffle is also built into the pick method on lists when you pass it a "whatever" for the number to pick:
my @deck = @cards.pick(*);
Phix
sequence cards = tagset(52)
puts(1,"Before: ") ?cards
for i=52 to 1 by -1 do
integer r = rand(i)
{cards[r],cards[i]} = {cards[i],cards[r]}
end for
puts(1,"After: ") ?cards
puts(1,"Sorted: ") ?sort(cards)
Before: {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52}
After: {42,4,48,28,11,3,52,51,22,2,49,38,25,33,27,35,18,44,5,7,21,13,36,29,43,6,9,31,10,30,20,16,46,34,8,17,14,45,37,24,32,41,50,15,39,40,47,23,1,12,26,19}
Sorted: {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52}
```
## PHP
```php
//The Fisher-Yates original Method
function yates_shuffle($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) )
```
```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;
```
```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
```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())
```
```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)
```
```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:
```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()
```
```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
```
```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
```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
```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;
```
```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))
```
```txt
[7, 4, 3, 8, 9, 6, 10, 2, 1, 5]
```
## 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
```
```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())
```
```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 {
let j = i0.advancedBy(numericCast(
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]))
```
```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 {
let j = i0.advancedBy(numericCast(
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())
```
```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
```
```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
```
```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
```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'
```
```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
```
```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, ", " )
```
```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)
```
```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")
```