- array_map: documentation ( source)
- var_dump: documentation ( source)
- strpos: documentation ( source)
- array_filter: documentation ( source)
<?php
$array = array('1', '1a', '2a', '3', '4a');
$array2 = array_map(function($val) { return strpos($val, 'a') ? $val : null; }, $array);
var_dump(array_filter($array2));