Generate array of random unique numbers in PHP

Question

I\'m trying to generate an array of random numbers from 0-n then shuffle (but ensure that the keys and values DO NOT match).

For example:

0 => 3
1         


        

Answer 1

Here's a rather long, but also pretty efficient solution, I believe. Contrary to other solutions posted here, this cannot deadlock (unless $size<2), and this will not do a full shuffle every time one value doesn't fit. Instead, it will only replace that value with another, random value.

function unique_list($size=5) {

    function all_unique($numbers) {
        foreach ($numbers as $key=>$value)
            if ($key==$value) return false;
        return true;
    }
    function flip($a, $b, &$numbers) {
        $numbers[$a] = $numbers[$a] + $numbers[$b];
        $numbers[$b] = $numbers[$a] - $numbers[$b];
        $numbers[$a] = $numbers[$a] - $numbers[$b];
    }

    $flip_count = 0;
    $numbers = range(0,$size-1);
    shuffle($numbers);

    while (!all_unique($numbers)) {
        foreach ($numbers as $key=>$value) {
            if ($key==$value) {
                flip($key, rand(0,$size-1), $numbers);
                $flip_count++;
                break;
            }
        }
    }

    printf("Flipped %d values\n", $flip_count);
    return $numbers;

}

$list = unique_list(10);
print_r($list);

The above will print something similar to

Flipped 1 value(s)
Array
(
    [0] => 2
    [1] => 5
    [2] => 7
    [3] => 9
    [4] => 6
    [5] => 3
    [6] => 1
    [7] => 8
    [8] => 0
    [9] => 4
)