If you want to sort an array according to another array acting as a priority list, you can use this function.

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

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

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

$order[0] = "first";
$order[1] = "second";
$order[2] = "third";

$array[0] = "second";
$array[1] = "first";
$array[2] = "third";
$array[3] = "fourth";
$array[4] = "second";
$array[5] = "first";
$array[6] = "second";

usort($array, "listcmp");

print_r($array);
?>