- var_dump: documentation ( source)
- explode: documentation ( source)
- sort: documentation ( source)
- array_diff: documentation ( source)
<?php
$relate_to = [11,22];
$before = NULL;
$relate_to_before = explode(',', $before);
sort($relate_to_before);
$relate_to_new = array_diff($relate_to, $relate_to_before);
var_dump($relate_to_new);