array_rand

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

array_rand — 从数组中随机取出一个或多个随机键

说明

array_rand ( array $array , int $num = 1 ) : int|string|array

从数组中取出一个或多个随机的单元，并返回随机条目对应的键（一个或多个）。它使用了伪随机数产生算法，所以不适合密码学场景。

参数

array: 输入的数组。
num: 指定要取出的单元数量。

返回值

如果只取出一个，array_rand() 返回随机单元的键名。否则就返回包含随机键名的数组。完成后，就可以根据随机的键获取数组的随机值。如果返回的是包含随机键名的数组，数组单元的顺序按照键名在原数组中的顺序排列。取出数量如果超过 array 的长度，就会导致 E_WARNING 错误，并返回 NULL。

更新日志

版本	说明
7.1.0	内部随机化算法已从 libc rand 函数更改为使用 » 梅森旋转算法（Mersenne Twister）随机数生成器。

范例

Example #1 array_rand() 例子


<?php
$input = array("Neo", "Morpheus", "Trinity", "Cypher", "Tank");
$rand_keys = array_rand($input, 2);
echo $input[$rand_keys[0]] . "\n";
echo $input[$rand_keys[1]] . "\n";
?>

参见

shuffle() - 打乱数组

User Contributed Notes

fulachan2 at gmail dot com 30-Sep-2021 07:45


array_rand () takes a random value without ever being able to go back in its choice of random value.

A simple example:

I decide to mix an array of 10 entries to retrieve 3 values. This choice will give increasing and random values.



    $myarray = range(1,10);

    

    $pm = array_rand($myarray,3);      

    // $pm return array(0->0,1->6,2->8)



But if I decide to shuffle an array of 10 entries to get 10 entries, array_rand () will choose to assign a value to each return value and therefore the return array will not be random.



    $gm = array_rand($myarray,count($myarray)); 

    // $gm not random array(0->0,1->1,2->2,3->3,4->4,5->5,6->6,7->7,8->8,9->9)



The easiest way to have a truly random value:

either use array_rand () in a loop of 1 value at a time



$deg = range(-60,60);

$size = range(16,64);

$color = ["blue","red","green","pink","orange","purple","grey","darkgreen","darkkhaki"];

$i = 0;

$longueur = 10;

do{

    ++$i;

    printf("<span style='transform: rotateZ(%ddeg); display: inline-block;font-size: %spx; color:%s'>%s</span>",

        $deg[array_rand($deg)],

        $size[array_rand($size)],

        $color[array_rand($color)],

        $alnum[array_rand($alnum)]);



}while($i < $longueur);



------------------

or simply use shuffle () to shuffle the array really randomly.

grzeniufication 03-Mar-2018 10:19


<?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)]);

}

grzeniufication 03-Mar-2018 09:22


<?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 ) ) ) ) );

Anonymous 13-Jul-2012 02:42


It doesn't explicitly say it in the documentation, but PHP won't pick the same key twice in one call.

Anonymous 02-Oct-2009 01:04


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); ?>