- array_map: documentation ( source)
- implode: documentation ( source)
- explode: documentation ( source)
- strrev: documentation ( source)
<?php
$input = "30.10.2012";
$input = "2012-10-30";
$reverse = true;
$inputSplitChar = $reverse === false ? '.' : '-';
$OutputSplitChar = $reverse === false ? '-' : '.';
$resultArray = array_map('strrev', explode($inputSplitChar, strrev($input)));
$result = implode($OutputSplitChar, $resultArray);
echo $result;