shuffle

(PHP 4, PHP 5, PHP 7, PHP 8)

shuffleShuffle an array

Description

shuffle(array &$array): true

This function shuffles (randomizes the order of the elements in) an array.

Caution

This function does not generate cryptographically secure values, and must not be used for cryptographic purposes, or purposes that require returned values to be unguessable.

If cryptographically secure randomness is required, the Random\Randomizer may be used with the Random\Engine\Secure engine. For simple use cases, the random_int() and random_bytes() functions provide a convenient and secure API that is backed by the operating system’s CSPRNG.

Parameters

array

The array.

Return Values

Always returns true.

Changelog

Version Description
7.1.0 The internal randomization algorithm has been changed to use the » Mersenne Twister Random Number Generator instead of the libc rand function.

Examples

Example #1 shuffle() example

<?php
$numbers
= range(1, 20);
shuffle($numbers);
foreach (
$numbers as $number) {
echo
"$number ";
}
?>

Notes

Note: This function assigns new keys to the elements in array. It will remove any existing keys that may have been assigned, rather than just reordering the keys.

Note:

Resets array's internal pointer to the first element.

See Also

add a note

User Contributed Notes 16 notes

up
131
ahmad at ahmadnassri dot com
14 years ago
shuffle for associative arrays, preserves key=>value pairs.
(Based on (Vladimir Kornea of typetango.com)'s function)

<?php
function shuffle_assoc(&$array) {
$keys = array_keys($array);

shuffle($keys);

foreach(
$keys as $key) {
$new[$key] = $array[$key];
}

$array = $new;

return
true;
}
?>

*note: as of PHP 5.2.10, array_rand's resulting array of keys is no longer shuffled, so we use array_keys + shuffle.
up
26
andjones at gmail dot com
13 years ago
Shuffle associative and non-associative array while preserving key, value pairs. Also returns the shuffled array instead of shuffling it in place.

<?php

function shuffle_assoc($list) {
if (!
is_array($list)) return $list;

$keys = array_keys($list);
shuffle($keys);
$random = array();
foreach (
$keys as $key)
$random[$key] = $list[$key];

return
$random;
}

?>
up
7
Anonymous
14 years ago
I needed a simple function two shuffle a two dimensional array. Please note the second level arrays must be indexed using integers, for example $myarray[0]["Name"] and not $myarray["One"]["Name"]. Here is the function:

<?php
function twodshuffle($array)
{
// Get array length
$count = count($array);
// Create a range of indicies
$indi = range(0,$count-1);
// Randomize indicies array
shuffle($indi);
// Initialize new array
$newarray = array($count);
// Holds current index
$i = 0;
// Shuffle multidimensional array
foreach ($indi as $index)
{
$newarray[$i] = $array[$index];
$i++;
}
return
$newarray;
}
?>

Please note it only works on two dimensional arrays. Here is an example:

<?php
$myarray
= array("Google" => array("Name" => "Google", "URL" => "www.google.com", "Usage" => "Googling"), "Yahoo" => array("Name" => "Yahoo", "URL" => "www.yahoo.com", "Usage" => "Yahooing?"), "Ask" => array("Name" => "Ask", "URL" => "www.ask.com", "Usage" => "Asking Jeeves"));

print_r(twodshuffle($myarray));

/* And the result is:
Array ( [0] => Array ( [Name] => Ask [URL] => www.ask.com [Usage] => Asking Jeeves ) [1] => Array ( [Name] => Google [URL] => www.google.com [Usage] => Googling ) [2] => Array ( [Name] => Yahoo [URL] => www.yahoo.com [Usage] => Yahooing? ) )
*/
?>

Hope you find it useful!
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9
dirk dot avery a t gmail
15 years ago
Building on examples by m227 and pineappleclock, here is a function that returns all permutations of each set in the power set of an array of strings (instead of a string). Thanks for the great examples!

<?php

/*
Use: $arr = power_perms($in);

Example:
$in = array("A","B","C");
$power_perms = power_perms($in);

Returns:
Array
(
[0] => Array
(
[0] => A
[1] => B
[2] => C
)

[1] => Array
(
[0] => A
[1] => C
[2] => B
)

[2] => Array
(
[0] => B
[1] => A
[2] => C
)

[3] => Array
(
[0] => B
[1] => C
[2] => A
)

[4] => Array
(
[0] => C
[1] => A
[2] => B
)

[5] => Array
(
[0] => C
[1] => B
[2] => A
)

[6] => Array
(
[0] => A
[1] => B
)

[7] => Array
(
[0] => B
[1] => A
)

[8] => Array
(
[0] => B
[1] => C
)

[9] => Array
(
[0] => C
[1] => B
)

[10] => Array
(
[0] => A
[1] => C
)

[11] => Array
(
[0] => C
[1] => A
)

[12] => Array
(
[0] => A
)

[13] => Array
(
[0] => B
)

[14] => Array
(
[0] => C
)

)

*/

function power_perms($arr) {

$power_set = power_set($arr);
$result = array();
foreach(
$power_set as $set) {
$perms = perms($set);
$result = array_merge($result,$perms);
}
return
$result;
}

function
power_set($in,$minLength = 1) {

$count = count($in);
$members = pow(2,$count);
$return = array();
for (
$i = 0; $i < $members; $i++) {
$b = sprintf("%0".$count."b",$i);
$out = array();
for (
$j = 0; $j < $count; $j++) {
if (
$b{$j} == '1') $out[] = $in[$j];
}
if (
count($out) >= $minLength) {
$return[] = $out;
}
}

//usort($return,"cmp"); //can sort here by length
return $return;
}

function
factorial($int){
if(
$int < 2) {
return
1;
}

for(
$f = 2; $int-1 > 1; $f *= $int--);

return
$f;
}

function
perm($arr, $nth = null) {

if (
$nth === null) {
return
perms($arr);
}

$result = array();
$length = count($arr);

while (
$length--) {
$f = factorial($length);
$p = floor($nth / $f);
$result[] = $arr[$p];
array_delete_by_key($arr, $p);
$nth -= $p * $f;
}

$result = array_merge($result,$arr);
return
$result;
}

function
perms($arr) {
$p = array();
for (
$i=0; $i < factorial(count($arr)); $i++) {
$p[] = perm($arr, $i);
}
return
$p;
}

function
array_delete_by_key(&$array, $delete_key, $use_old_keys = FALSE) {

unset(
$array[$delete_key]);

if(!
$use_old_keys) {
$array = array_values($array);
}

return
TRUE;
}
?>
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4
pineappleclock at gmail dot com
15 years ago
If you want the Power Set (set of all unique subsets) of an array instead of permutations, you can use this simple algorithm:

<?php
/**
* Returns the power set of a one dimensional array,
* a 2-D array.
* array(a,b,c) ->
* array(array(a),array(b),array(c),array(a,b),array(b,c),array(a,b,c))
*/
function powerSet($in,$minLength = 1) {
$count = count($in);
$members = pow(2,$count);
$return = array();
for (
$i = 0; $i < $members; $i++) {
$b = sprintf("%0".$count."b",$i);
$out = array();
for (
$j = 0; $j < $count; $j++) {
if (
$b{$j} == '1') $out[] = $in[$j];
}
if (
count($out) >= $minLength) {
$return[] = $out;
}
}
return
$return;
}
?>
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6
peter at removethisplease dot ddcrew dot com
10 years ago
This seems to do reasonably well as a shuffle() that preserves index assocation:

<?php
function ashuffle (&$arr) {
uasort($arr, function ($a, $b) {
return
rand(-1, 1);
});
}
?>

Obviously only works if PHP has closures enabled...
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2
xzero at elite7hackers dot net
9 years ago
There is an function which uses native shuffle() but preserves keys, and their order, so at end, only values are shuffled.

<?PHP
/**
* Array Quake - Give an array good quake so every value will endup with random given space.
* Keys, and their order are preserved.
* @author xZero <xzero@elite7hackers.net>
* @param array $array
* @return boolean false on failure
*/
function array_quake(&$array) {
if (
is_array($array)) {
$keys = array_keys($array); // We need this to preserve keys
$temp = $array;
$array = NULL;
shuffle($temp); // Array shuffle
foreach ($temp as $k => $item) {
$array[$keys[$k]] = $item;
}
return;
}
return
false;
}

// Example
$numbers = array(
'ZERO' => 0,
'ONE' => 1,
'TWO' => 2,
'THREE' => 3,
'FOUR' => 4,
'FIVE' => 5,
'SIX' => 6,
'SEVEN' => 7,
'EIGHT' => 8,
'NINE' => 9
);
echo
"\nBefore (original):\n";
print_r($numbers);
array_quake($numbers);
echo
"\n\nAfter (Array Quake);\n";
print_r($numbers);
echo
"\n";
?>

Result example:
Before (original):
Array
(
[ZERO] => 0
[ONE] => 1
[TWO] => 2
[THREE] => 3
[FOUR] => 4
[FIVE] => 5
[SIX] => 6
[SEVEN] => 7
[EIGHT] => 8
[NINE] => 9
)

After (Array Quake);
Array
(
[ZERO] => 4
[ONE] => 2
[TWO] => 0
[THREE] => 8
[FOUR] => 3
[FIVE] => 6
[SIX] => 1
[SEVEN] => 7
[EIGHT] => 5
[NINE] => 9
)
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3
tony at brokerbin dot com
15 years ago
Here is IMO the simplest and extremely fast way to shuffle an associative array AND keep the key=>value relationship. However, it ONLY works if there are NO NUMERIC keys AT ALL. Look into array_merge for the reason why.

<?php

$unshuffled
= array('one'=>1,'two'=>2,'three'=>3);

$shuffled = array_merge( array_flip(array_rand($unshuffled,count($unshuffled))),$unshuffled );

?>

peace
up
4
aalaap at gmail dot com
15 years ago
I've been wondering why shuffle() doesn't provide the shuffled array as a return value instead of a bool. I mean, what could possibly go wrong in shuffling elements from an array?

So I use something like this:

<?php
function array_shuffle($array) {
if (
shuffle($array)) {
return
$array;
} else {
return
FALSE;
}
}
?>
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2
ezakto at ezakto dot com
13 years ago
This is a replica of shuffle() but preserving keys (associative and non-associative)

bool kshuffle ( array &$array )

<?php

function kshuffle(&$array) {
if(!
is_array($array) || empty($array)) {
return
false;
}
$tmp = array();
foreach(
$array as $key => $value) {
$tmp[] = array('k' => $key, 'v' => $value);
}
shuffle($tmp);
$array = array();
foreach(
$tmp as $entry) {
$array[$entry['k']] = $entry['v'];
}
return
true;
}

$array = array('first' => 0, 'second' => 1, 'third' => 2);
kshuffle($array);
print_r($array); // [second] => 1 [first] => 0 [third] => 2

$array = array('first', 'second', 'third');
kshuffle($array);
print_r($array); // [1] => second [2] => third [0] => first

?>
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3
rick at suggestive dot com
14 years ago
Many people in SEO need to supply an array and shuffle the results and need the same result each time that page is generated. This is my implementation with a working example:

<?php
function seoShuffle(&$items,$string) {
mt_srand(strlen($string));
for (
$i = count($items) - 1; $i > 0; $i--){
$j = @mt_rand(0, $i);
$tmp = $items[$i];
$items[$i] = $items[$j];
$items[$j] = $tmp;
}
}

$items = array('one','two','three','four','five','six');
$string = 'whatever';

echo
'<pre>';
print_r($items);
echo
'</pre>';

seoShuffle($items,$string);

echo
'<pre>';
print_r($items);
echo
'</pre>';
?>
up
2
sivaji2009 at gmail dot com
15 years ago
Here i wrote a custom shuffle function which preserves the array index and distributes the array element randomly.

<?php

/*
* return an array whose elements are shuffled in random order.
*/
function custom_shuffle($my_array = array()) {
$copy = array();
while (
count($my_array)) {
// takes a rand array elements by its key
$element = array_rand($my_array);
// assign the array and its value to an another array
$copy[$element] = $my_array[$element];
//delete the element from source array
unset($my_array[$element]);
}
return
$copy;
}

$array = array(
'a' => 'apple',
'b' => 'ball',
'c' => 'cat',
'd' => 'dog',
'e' => 'egg',
'f' => 'fan',
'g' => 'gun'
);

print_r(custom_shuffle($array));

Array
(
[
c] => cat
[e] => egg
[f] => fan
[a] => apple
[b] => ball
[g] => gun
[d] => dog
)

?>
up
2
Eric Anderson
13 years ago
Copy and paste this script and refresh the page to see the shuffling effect.

<?php
/**
* Shuffles and displays cards in a deck
* @author: Eric Anderson
* @filename: deckofcards.php
*/

// Create an array of face values
// and an array of card values
// then merge them together
$cards = array_merge(array("J", "Q", "K", "A"), range(2,10)); // 13 cards

// Shuffle the cards
shuffle($cards);

// Create an multidimentional array to hold the 4 suits
$suits = array(
'Heart' => array(),
'Spade' => array(),
'Diamond' => array(),
'Club' => array()
);

// Add cards to their respective suits
for($i = 0; $i < count($suits); $i++)
{
for(
$j = 0; $j < count($cards); $j++)
{
$suits['Heart'][$j] = $cards[$j]."<span style=color:#FF0000;>&hearts;</span>";
$suits['Spade'][$j] = $cards[$j]."&spades;";
$suits['Diamond'][$j] = $cards[$j]."<span style=color:#FF0000;>&diams;</span>";
$suits['Club'][$j] = $cards[$j]."&clubs;";
}
}

// Create a deck
$deck = array();

// Merge the suits into the empty deck array
$deck = array_merge($deck, $suits);

// Display the deck to the screen
echo "<p><b>Deck of cards:</b></p>";
foreach(
$deck as $k1 => $v1)
{
// Display suit name
echo "<p>&emsp;$k1's<br />&emsp;{<br />&emsp;&emsp;";
$acc = 0;

// Display card value
foreach($v1 as $k2 => $v2)
{
echo
"$v2&nbsp";
$acc++;

if (
$acc == 4)
{
echo
"<br />&emsp;&emsp;";
$acc = 0;
}
}
echo
"<br />&emsp;}</p>";
}
?>
up
2
tyler at CompLangs dot com
14 years ago
Here is a quick function I wrote that generates a random password and uses shuffle() to easily shuffle the order.

<?php
public function randPass($upper = 3, $lower = 3, $numeric = 3, $other = 2) {
//we need these vars to create a password string
$passOrder = Array();
$passWord = '';

//generate the contents of the password
for ($i = 0; $i < $upper; $i++) {
$passOrder[] = chr(rand(65, 90));
}
for (
$i = 0; $i < $lower; $i++) {
$passOrder[] = chr(rand(97, 122));
}
for (
$i = 0; $i < $numeric; $i++) {
$passOrder[] = chr(rand(48, 57));
}
for (
$i = 0; $i < $other; $i++) {
$passOrder[] = chr(rand(33, 47));
}

//randomize the order of characters
shuffle($passOrder);

//concatenate into a string
foreach ($passOrder as $char) {
$passWord .= $char;
}

//we're done
return $passWord;
}
?>
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1
Antonio Ognio
16 years ago
Another shuffle() implementation that preserves keys, does not use extra memory and perhaps is a bit easier to grasp.

<?php
if (function_exists('shuffle_with_keys')===false) {
function
shuffle_with_keys(&$array) {
/* Auxiliary array to hold the new order */
$aux = array();
/* We work with an array of the keys */
$keys = array_keys($array);
/* We shuffle the keys */
shuffle($keys);
/* We iterate thru' the new order of the keys */
foreach($keys as $key) {
/* We insert the key, value pair in its new order */
$aux[$key] = $array[$key];
/* We remove the element from the old array to save memory */
unset($array[$key]);
}
/* The auxiliary array with the new order overwrites the old variable */
$array = $aux;
}
}
?>
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0
DiosDe
2 years ago
implementation of shuffle() using random_int()

<?php

function random_int_shuffle ( array $array ): array
{
$array = array_values($array);

$result = [];
$skip_indexes = [];

$sizeof_array = count($array);

for (
$i = 0; $i < $sizeof_array; $i++ )
{
do
{
$random_index = random_int(0, $sizeof_array);
} while (
in_array($random_index, $skip_indexes) );

$skip_indexes[] = $random_index;
$result[] = $array[$random_index];
}

return
$result;
}
?>
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