title: Sum up column values in Pandas DataFrame
body: <p>In a pandas DataFrame, is it possible to collapse columns which have identical values, and sum up the values in another column?</p>
  
  <p><strong>Code</strong></p>
  
  <pre><code>data = {"score":{"0":9.397,"1":9.397,"2":9.397995,"3":9.397996,"4":9.3999},"type":{"0":"advanced","1":"advanced","2":"advanced","3":"newbie","4":"expert"},"count":{"0":394.18930604,"1":143.14226729,"2":9.64172783,"3":0.1,"4":19.65413734}}
  df = pd.DataFrame(data)
  df
  </code></pre>
  
  <p><strong>Output</strong></p>
  
  <pre><code>     count       score       type
  0    394.189306  9.397000    advanced
  1    143.142267  9.397000    advanced
  2    9.641728    9.397995    advanced
  3    0.100000    9.397996    newbie
  4    19.654137   9.399900    expert
  </code></pre>
  
  <p>In the example above, the first two rows have the same <code>score</code> and <code>type</code> , so these rows should be merged together and their scores added up.</p>
  
  <p><strong>Desired Output</strong></p>
  
  <pre><code>     count       score       type
  0    537.331573  9.397000    advanced
  1    9.641728    9.397995    advanced
  2    0.100000    9.397996    newbie
  3    19.654137   9.399900    expert
  </code></pre>