laravel how to get all nested relation to a collection

So lets say i have a post which belong to 1 user which belong to 1 group;

now I getting all the posts:

$posts = Post::inCategory(1)->with('user','user.group')->get();

now I need to see all groups in the above query, is there some simple 1 liner collection trick to extract them? without looping like:

$groups = [];
foreach ($posts as $post){
 $groups[] = $post->user->group;
}

via Chebli Mohamed