<?php
$array = array("2011-September_38","2011-June_4","2009-May_3","2009-May_45","2010-March_2","2010-November_9","2011-December_29","2010-March_19");
function yearmonthCompare($a, $b) {
$count = substr($a,strpos($a,'_'));
$count =strlen($count);
$count1 = substr($b,strpos($b,'_'));
$count1 =strlen($count1);
$da = strtotime(substr($a,0,-$count));
$db = strtotime(substr($b,0,-$count1));
return $da > $db;
}
usort($array, "yearmonthCompare");
foreach($array as $sorter)
{
$ids[] = explode("_",$sorter);
}
print_r($ids);
?>