Sorting array based on key string

Pardon my sloppy explanation but here it is: how can i sort an array based on key element ie. key values are: a1, a2 ,a3 ..., b1, b2 ,b3, ...c1, c1, c3... so doing this: while (list($k, $v) = each($data)) { for ($i=0; $i<count($k); $i++) { echo "$k[0] = $v\n<br>"; } will list all the $k $v . a = foo a = bar b = another foo ....... and so on Now, how can i sort it according to $k[0] where $k[0] = a, than the same for all b's and so on.