Membalik Array

<?php
$data = array('RT III' => 3,'RT II' => 2,'RT I' => 2,'RT V' => 1,'RT IV' => 1);
print_r($data);
foreach($data as $key=>$val){
    $data2[$val][] = $key;
}
foreach($data2 as $key2=>$val2)
    echo "$key2 => ",implode(', ',$val2),"<br />";

?>