<?php
 
function x($k1, $k2) {
     if ($k1 == $k2)
         return 0;
     else if (k1 > $k2)
         return 1;
     else
         return -1
}
 
$x1 = array('blue'  => 1, 'red'  => 2, 'green'  => 3, 'purple' => 4);
$x2 = array('green' => 5, 'blue' => 6, 'yellow' => 7, 'cyan'   => 8);
 
var_dump(array_intersect_ukey($x1, $x2, 'x'));

?>