- print_r: documentation ( source)
- preg_match_all: documentation ( source)
- array_filter: documentation ( source)
<?php
$re = '/([\D]+)|([\d]+)/';
$str = 'a74b8c0d3845e7';
preg_match_all($re, $str, $matches);
print_r(array_filter($matches[1]));print_r($matches[2]);