- var_dump: documentation ( source)
- array_merge: documentation ( source)
- array_keys: documentation ( source)
<?php
$arr1 = ["apple" => "bla", "peer" => "bleh"];
$arr2 = ["apple" => "foo", "bar" => "baz"];
$totalKeys = array_merge(array_keys($arr1), array_keys($arr2));
var_dump($totalKeys);