- print_r: documentation ( source)
- array_diff: documentation ( source)
- array_walk: documentation ( source)
<?php
$ids=array("a","b","c","d","e");
$groups=array(array("a","c"),array("c","e"));
array_walk($groups,function($v,$i)use(&$ids){
$ids=array_diff($ids,$v);
});
print_r($ids);