- var_dump: documentation ( source)
- array_diff_key: documentation ( source)
<?php
$array1 = array("a" => "green", "b" => "brown", "c" => "blue", "red");
$array2 = array("a" => "green", "b" => "yellow", "red");
$result = array_diff_key($array1, $array2);
var_dump($result, $array1, $array2);