- array_map: documentation ( source)
- print_r: documentation ( source)
- array_keys: documentation ( source)
<?php
$ar = array('a' => 'b');
function cb($v) { return $v; }
function keys($v, $k) { return $k; }
print_r(array_map('cb', $ar));
$keys = array_map('keys', $ar, array_keys($ar));
print_r(array_map('cb', $ar, $keys));