I'm using RecursiveDirectoryIterator and RecursiveIteratorIterator to build a file listing tree using code like below. I need to the list to be sorted - either directories then files alphabetically, or just alphabetically.

Can anyone tell me how to sort the file list?

$dir_iterator = new RecursiveDirectoryIterator($groupDirectory);
$iterator = new RecursiveIteratorIterator($dir_iterator, RecursiveIteratorIterator::SELF_FIRST);
foreach ($iterator as $file) {
    // do stuff with $file
}