<?php
$arr1 = array(
    "k1" => "v1",
    "k2" => "v2",
    "k3" => "v3",
    "k4" => "v4",
    "k5" => "v5"
);

$arr2 = array(
    "k1" => "v4",
    "k2" => "v5"
);

echo("Using 'array_diff':\n");
var_dump(array_diff($arr1, $arr2));
echo("Using 'array_diff_key':\n");
var_dump(array_diff_key($arr1, $arr2));