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array_rand

(PHP 4, PHP 5, PHP 7)

array_randPick one or more random keys out of an array

Descrierea

array_rand ( array $array [, int $num = 1 ] ) : mixed

Picks one or more random entries out of an array, and returns the key (or keys) of the random entries. It uses a pseudo random number generator that is not suitable for cryptographic purposes.

Parametri

array

The input array.

num

Specifies how many entries should be picked.

Valorile întoarse

When picking only one entry, array_rand() returns the key for a random entry. Otherwise, an array of keys for the random entries is returned. This is done so that random keys can be picked from the array as well as random values. Trying to pick more elements than there are in the array will result in an E_WARNING level error, and NULL will be returned.

Istoricul schimbărilor

Versiune Descriere
7.1.0 The internal randomization algorithm has been changed to use the » Mersenne Twister Random Number Generator instead of the libc rand function.
5.2.10 The resulting array of keys is no longer shuffled.

Exemple

Example #1 array_rand() example

<?php
$input 
= array("Neo""Morpheus""Trinity""Cypher""Tank");
$rand_keys array_rand($input2);
echo 
$input[$rand_keys[0]] . "\n";
echo 
$input[$rand_keys[1]] . "\n";
?>

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User Contributed Notes 4 notes

up
52
Anonymous
11 years ago
If the array elements are unique, and are all integers or strings, here is a simple way to pick $n random *values* (not keys) from an array $array:

<?php array_rand(array_flip($array), $n); ?>
up
22
grzeniufication
2 years ago
<?php
// An example how to fetch multiple values from array_rand
$a = [ 'a', 'b', 'c', 'd', 'e', 'f', 'g' ];
$n = 3;

// If you want to fetch multiple values you can try this:
print_r( array_intersect_key( $a, array_flip( array_rand( $a, $n ) ) ) );

// If you want to re-index keys wrap the call in 'array_values':
print_r( array_values( array_intersect_key( $a, array_flip( array_rand( $a, $n ) ) ) ) );
up
14
grzeniufication
2 years ago
<?php

/**
* Wraps array_rand call with additional checks
*
* TLDR; not so radom as you'd wish.
*
* NOTICE: the closer you get to the input arrays length, for the n parameter, the  output gets less random.
* e.g.: array_random($a, count($a)) == $a will yield true
* This, most certainly, has to do with the method used for making the array random (see other comments).
*
* @throws OutOfBoundsException – if n less than one or exceeds size of input array
*
* @param array $array – array to randomize
* @param int $n – how many elements to return
* @return array
*/
function array_random(array $array, int $n = 1): array
{
    if (
$n < 1 || $n > count($array)) {
        throw new
OutOfBoundsException();
    }

    return (
$n !== 1)
        ?
array_values(array_intersect_key($array, array_flip(array_rand($array, $n))))
        : array(
$array[array_rand($array)]);
}
up
12
Anonymous
8 years ago
It doesn't explicitly say it in the documentation, but PHP won't pick the same key twice in one call.
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