title: Pandas group by will not work
body: <p>what am i missing here?  I am trying to do a group by.</p>
  
  <pre><code>asp = np.array(np.array([0,0,1]))
  asq = np.array(np.array([10,10,20]))
  columns=['asp']
  df = pd.DataFrame(asp, index=None, columns=columns)
  df['asq'] = asq
  print df
  df.groupby(by=['asp']).sum()
  print df
     asp  asq
  0    0   10
  1    0   10
  2    1   20
     asp  asq
  0    0   10
  1    0   10
  2    1   20
  </code></pre>
  
  <p>results should be:</p>
  
  <pre><code>    asp  asq
  0    0   20
  1    1   20
  </code></pre>