title: Group by based on a value of a column
body: <p>i have the following DataFrame:</p>
  
  <p><a href="https://i.stack.imgur.com/M0whx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/M0whx.png" alt="enter image description here"></a></p>
  
  <p>it contains user_ids, tweets, and the classification of the tweet as negative and positive.</p>
  
  <p>i want to create a new dataframe that has the following columns:</p>
  
  <ol>
  <li>user_id</li>
  <li>count of negative tweets by that user_id</li>
  <li>count of positive tweets by that user_id</li>
  </ol>
  
  <p>Thanks</p>