shuffle

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

shuffle — Shuffle 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.

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User Contributed Notes 16 notes

down

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.

down

andjones at gmail dot com ¶

14 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;

}



?>

down

Anonymous ¶

15 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!

down

dirk dot avery a t gmail ¶

15 years ago

down

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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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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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
)

down

tony at brokerbin dot com ¶

16 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

down

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;

    }

}

?>

down

ezakto at ezakto dot com ¶

14 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

?>

down

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>';

?>

down

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
)

?>

down

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>";

    }

?>

down

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;

}

?>

down

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;

  }

}

?>

down

DiosDe ¶

3 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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shuffle

Description

Parameters

Return Values

Changelog

Examples

Notes

See Also

Improve This Page

User Contributed Notes 16 notes