usort-example

<?php
function list_cmp($a, $b) {
    global $order;

    foreach ($order as $key => $value) {
        if ($a == $value) {
            return 0;
        }

        if ($b == $value) {
            return 1;
        }
    }
}

$order[0] = 1;
$order[1] = 3;
$order[2] = 4;
$order[3] = 2;

$array[0] = 2;
$array[1] = 1;
$array[2] = 3;
$array[3] = 4;
$array[4] = 2;
$array[5] = 1;
$array[6] = 2;

usort($array, "list_cmp");