title: How to merge rows with same index on a single data frame?
body: <p>I have a dataframe that looks like this:</p>
  
  <pre><code>A          B           C
  1          1234        Win
  1          2345        Win
  2          1987        Loss
  3          3456        Win
  3          4567        Win
  </code></pre>
  
  <p>And I want this to become:</p>
  
  <pre><code>A          B           C
  1          1234,2345   Win
  2          1987        Loss
  3          3456,4567   Win
  </code></pre>
  
  <p>Note: C values always have the same value for the same index.</p>
  
  <p>Anyone can help? Thanks!</p>