title: Sum list of values within a pandas df
body: <p>I'm sure this could be somewhere in <code>SO</code> but I can't seem to find it. I am trying to <code>sum</code> values expressed within <code>lists</code> from a <code>pandas</code> <code>df</code>. Example</p>
  
  <p>I can achieve this using this following from an <code>array</code>:</p>
  
  <pre><code>array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
  
  array = [sum(a) for a in zip(*array)]
  </code></pre>
  
  <p>But when the values are housed within a <code>df</code> I can't get it working. Here is my attempt:</p>
  
  <pre><code>d = ({
      'Val' : [[1,2,3],[4,5,6],[7,8,9]],   
       })
  
  df = pd.DataFrame(data = d)
  
  df = [sum(a) for a in zip(df['Val'])]
  
  print(df)
  
  df = [sum(a) for a in zip(df['Val'])]
  
  TypeError: unsupported operand type(s) for +: 'int' and 'list'
  </code></pre>