- array_map: documentation ( source)
- array_count_values: documentation ( source)
- print_r: documentation ( source)
- array_filter: documentation ( source)
<?php
$stack = array("twice", "twice", "once", "another once");
print_r(array_filter(array_map((function ($v) { return $v > 1 ? $v : 0; }), array_count_values($stack))));