Get random key from array due to weight in value.

array_rand_weight.php

<?php

function array_rand_weight(array $array)
{
    reset($array);

    $pointer = mt_rand(0, array_sum($array));
    if(!$pointer) {
        return key($array);
    }

    $accumulator = 0;

    while($accumulator < $pointer) {
        $key = key($array);
        $weight = current($array);
        $accumulator += $weight;
        next($array);
    }

    return $key;
}

/**
 * Test
 */

$array = array(
    'apple'     => 40,
    'orange'    => 30,
    'lemon'     => 20,
    'tomato'    => 7,
    'potato'    => 3,
);

$stat = array();

for($i = 0; $i < 10000; $i++) {
    $key = array_rand_weight($array);

    if(!isset($stat[$key])) {
        $stat[$key] = 0;
    }

    $stat[$key]++;
}

arsort($stat);
$weightSum = array_sum($stat);
foreach($stat as $key => $weight) {
    echo $key . ' => ' . $weight . ' (' . floor($weight / $weightSum * 100) . '%)' . PHP_EOL;
}

/**
 * Results:
 *
 * apple => 4107 (41%)
 * orange => 2920 (29%)
 * lemon => 1991 (19%)
 * tomato => 693 (6%)
 * potato => 289 (2%)
*/

Currently implemented in https://github.com/sokil/php-structure/blob/master/src/WeightList.php