Как преобразовать массив в список директорий и поддиректорий?

$folders = [
    (object) ['id' => 1, 'parent' => 0, 'name' => 'foo'],
    (object) ['id' => 2, 'parent' => 1, 'name' => 'bar']
];

var_dump(folderpath($folders));

function folderpath(&$folders, $parent = 0) {
    $path = [];
    foreach ($folders as $id => $data) {
        if ($data->parent == $parent) {
            $path[] = $data->name;
            $sub = folderpath($folders, $data->id);
            if (strlen($sub) > 0) {
                $path[] = $sub;
            }
        }
    }
    return implode(DIRECTORY_SEPARATOR, $path);
}

$folders = [
    (object) ['id' => 1, 'parent' => 0, 'name' => 'foo'],
    (object) ['id' => 2, 'parent' => 1, 'name' => 'bar'],
    (object) ['id' => 3, 'parent' => 0, 'name' => 'foo2'],
    (object) ['id' => 4, 'parent' => 3, 'name' => 'bar2']
];

var_dump(folderpath($folders));

function folderpath($folders) {
    $out = [];
    foreach ($folders as $id => $data) {
        $path = [];
        if ($data->parent == $parent) {
            $path[] = $data->name;
            $sub = folderpathrec($folders, $data->id);
            if (strlen($sub) > 0) {
                $path[] = $sub;
            }
        }
        if (count($path) > 0) {
            $out[] = implode(DIRECTORY_SEPARATOR, $path);
        }
    }
    return $out;
}

function folderpathrec($folders, $parent = 0) {
    $path = [];
    foreach ($folders as $id => $data) {
        if ($data->parent == $parent) {
            $path[] = $data->name;
            $sub = folderpathrec($folders, $data->id);
            if (strlen($sub) > 0) {
                $path[] = $sub;
            }
        }
    }
    return implode(DIRECTORY_SEPARATOR, $path);
}