- var_dump: documentation ( source)
- decbin: documentation ( source)
- array_filter: documentation ( source)
<?php
$arr = ['x', 'y', 'z'];
$mask = 5;
$keys = decbin($mask);
$i = 0;
$result = array_filter($arr, function($val) use($keys, &$i) { return (bool)$keys[$i++]; });
var_dump($result);