title: Splitting values in index of a pandas dataframe
body: <p>I have a dataframe of this type: </p>
  
  <pre><code>d = {'a': [100,150,180,190]}
  df = pd.DataFrame(data=d, index=[(2010,1) ,(2010,2 ), (2011,1) ,(2011,2 )])
  </code></pre>
  
  <p>Which returns </p>
  
  <pre><code>Out[91]: 
               a
  (2010, 1)  100
  (2010, 2)  150
  (2011, 1)  180
  (2011, 2)  190
  </code></pre>
  
  <p>My scope is to split the values in the index and make the dataframe more readable by preserving the information of the index. In other words, my expected outcome is this:</p>
  
  <pre><code>dd = {'a': [100,150,180,190], 'year': [2010, 2011, 2010,2011], 'class': [1,2, 1,2]}
  df2 = pd.DataFrame(data=dd)
  
  Out[92]: 
       a  year  class
  0  100  2010      1
  1  150  2011      2
  2  180  2010      1
  3  190  2011      2
  </code></pre>
  
  <p>Any help ? </p>