title: Pandas: Convert dataframe to dict of lists
body: <p>I have a dataframe like this:</p>
  
  <pre><code>col1, col2
  A      0
  A      1
  B      2
  C      3
  </code></pre>
  
  <p>I would like to get this:</p>
  
  <pre><code>{ A: [0,1], B: [2], C: [3] }
  </code></pre>
  
  <p>I tried:</p>
  
  <pre><code>df.set_index('col1')['col2'].to_dict()
  </code></pre>
  
  <p>but that is not quite correct. The first issue I have is 'A' is repeated, I end up getting A:1 only (0 gets overwritten). How to fix?  </p>