title: Pandas drop group column after groupby.apply(..)
body: <pre><code>        uid  iid  val
  uid                 
  1   1    1    5   5.5
  2   3    1    4   3.5
  2   2    1    4   3.5
  2   7    1    4   3.5
  2   9    1    4   3.5
  2   11   1    4   3.5
  </code></pre>
  
  <p>From the dataframe above, I want to remove the first column, which is:</p>
  
  <pre><code>uid
  1
  2
  2
  2
  2
  2
  </code></pre>
  
  <p>and extract</p>
  
  <pre><code>    uid  iid  val
  
  1    1    5   5.5
  3    1    4   3.5
  2    1    4   3.5
  7    1    4   3.5
  9    1    4   3.5
  11   1    4   3.5
  </code></pre>
  
  <p>Can someone help?</p>