title: Selecting one repeated column in a dataframe on pandas
body: <p>Having the following dataframe,</p>
  
  <pre><code>index c1 c1 c1 c2 c2 c2
  0     1  2  0  1  1  2
  1     2  1  1  0  0  2
  2     0  0  1  2  2  1
  </code></pre>
  
  <p>it's obvious that <code>df['c1']</code> returns</p>
  
  <pre><code>index c1 c1 c1
  0     1  2  0
  1     2  1  1
  2     0  0  1
  </code></pre>
  
  <p>Now, how do I select over those three columns? Slicing doesn't seem to get the job done...</p>
  
  <pre><code>idx = pd.IndexSlice
  df.loc[idx[:],idx[0]]
  </code></pre>
  
  <p>does return the same.</p>