title: Laravel 5.6 groupBy on collection doesn't work
body: <p>GroupBy just doesn't work on collection in Laravel 5.6, it is very annoying when simple things which supposed to work not wirking...</p>
  
  <pre><code>$users = Game::orderBy('game_count', 'desc')-&gt;get();
  
  $users_grouped = $users-&gt;groupBy('user_id');
  </code></pre>
  
  <p>As you might guess <code>$users_grouped</code> contains the same collection as <code>$users</code> with the same repeating <code>user_id</code> values.</p>
  
  <p>I don't get why it doesn't work as expected and how to fix it?</p>
  
  <p>At least <code>GROUP BY</code> works with raw DB select hopefully.. But I want to use Eloquent..</p>