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array_rand

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

array_rand Estrae a caso uno o più elementi da un array

Descrizione

array_rand(array $input, int $num_req = ?): mixed

array_rand() è piuttosto utile quando si vuole estrarre a caso uno o più elementi da un array. Prende un array (input) e un argomento ozpionale (num_req) che specifica quanti elementi estrarre - se non è specificato, è 1 per default.

Se si sta estraendo solo un elemento, array_rand() restituisce la chiave di un elemento. Altrimenti, restituisce un array di chiavi. Questo viene fatto in modo da permettere di estrarre dall'array sia le chiavi che i valori.

Nota: Dal PHP 4.2.0, non c'è più bisogno di inizializzare il generatore di nomeri casuali con srand() o mt_srand() dal momento che questo viene fatto automaricamente.

Example #1 esempio di array_rand()

<?
srand((float) microtime() * 10000000);
$input = array("Neo", "Morpheus", "Trinity", "Cypher", "Tank");
$chiavi = array_rand($input, 2);
echo $input[$chiavi[0]] . "\n";
echo $input[$chiavi[1]] . "\n";
?>

Vedere anche shuffle().

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User Contributed Notes 6 notes

up
94
Anonymous
15 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
72
Anonymous
12 years ago
It doesn't explicitly say it in the documentation, but PHP won't pick the same key twice in one call.
up
22
grzeniufication
6 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
10
grzeniufication
6 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
1
fulachan2 at gmail dot com
3 years ago
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.
up
0
divinity76+spam at gmail dot com
2 years ago
for a cryptographically secure version, try

<?php

/**
* fetch a random key from array, using a cryptograpically secure rng
* discussed+reviewed at https://codereview.stackexchange.com/questions/275832/cryptographically-secure-version-of-the-core-array-rand-function/
*
* @param array $array
* @throws ValueError if array is empty
* @return int|string key
*/
function array_rand_cryptographically_secure(array $array)/*: int|string*/ {
$max = count ( $array ) - 1;
if (
$max < 0) {
throw new
ValueError ( 'Argument #1 ($array) cannot be empty' );
}
return
key ( array_slice ( $array, random_int ( 0, $max ), 1, true ) );
}

$tests = [
[
5, 6, 7],
[
'a' => 1, 'b' => 2, 'c' => 3],
[
'zero', 4 => 'four', 9 => 'nine'],
[
"PEAN"=>0],
[]
];
foreach (
$tests as $test) {
echo
array_rand_cryptographically_secure($test) . "\n";
}

?>
(this is an improved version, which unlike the first version, avoids copying *all* the keys)
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