Group by two or multiple columns in Laravel

1// group by user_id, which is column name on posts table
2$posts = Post::with('author')->get()->groupBy('user_id');
3 
4// group by also accepts function: group by author name (author is relationship on posts model)
5$posts = Post::with('author')->get()->groupBy(fn($post) => $post->author->name);

1// group by author name and published year
2$posts = Post::with('author')->get()
3    ->groupBy([fn($post) => $post->author->name, fn($post) => $post->published_at->year]);
4 
5dd($posts)