- array_intersect_key: documentation ( source)
- print_r: documentation ( source)
- array_flip: documentation ( source)
- explode: documentation ( source)
<?php
$str = "1,5";
$base = array('1'=>'Bread','5'=>'Butter');
$replacements = array_intersect_key( $base, array_flip( explode(',', $str)));
print_r( $replacements);