PHP Manual: shuffle

Description

function 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.

Caution

This function uses the global Mt19937 (“Mersenne Twister”) instance as the source of randomness and thus shares its state with all other functions using the global Mt19937. Using any of these functions advances the sequence for all the other functions, regardless of scope.

Generating repeatable sequences by seeding mt_srand() or srand() with a known value will also yield repeatable output from this function.

Prefer using Random\Randomizer methods in all newly written code.

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.

shuffle