- var_dump: documentation ( source)
- array_keys: documentation ( source)
- array_diff: documentation ( source)
<?php
$arr1 = ['test' => 'test', 'yup' => 'nope', 'dick' => 'fart'];
$arr2 = ['test', 'yup', 'yolo'];
$diff = array_diff(array_keys($arr1), $arr2);
var_dump($diff);