--TEST-- Function -- array_diff_ukey --SKIPIF-- --FILE-- $key2) { return 1; } else { return -1; } } $array1 = array('blue' => 1, 'red' => 2, 'green' => 3, 'purple' => 4); $array2 = array('green' => 5, 'blue' => 6, 'yellow' => 7, 'cyan' => 8); print_r(array_diff_ukey($array1, $array2, 'key_compare_func')); ?> --EXPECT-- Array ( [red] => 2 [purple] => 4 )