Example to only return directories that are a specified depth in a tree:

<?php
function directory_mapper($path)
{
    $maxDepth = 3;
    $minDepth = 3;
    $iterator = new RecursiveIteratorIterator(
        new RecursiveDirectoryIterator($path, RecursiveDirectoryIterator::SKIP_DOTS),
        RecursiveIteratorIterator::SELF_FIRST,
        RecursiveIteratorIterator::CATCH_GET_CHILD// Ignore "Permission denied"
    );
    $iterator->setMaxDepth($maxDepth);

    $paths = array($path);
    foreach ($iterator as $path => $dir) {
        if ($iterator->getDepth() >= $minDepth) {
            if ($dir->isDir()) {
                $paths[] = $path;
            }
        }

    }
    array_shift($paths);
    return $paths;
}
?>