title: How to select rows in the last key of first level in a Multiindex dataframe?
body: <p>I have a Pandas DataFrame that looks like the following:</p>
  
  <pre><code>                       data
  date       signal                     
  2012-11-01 a           0.04
             b           0.03
  2012-12-01 a          -0.01
             b           0.00
  2013-01-01 a          -0.00
             b          -0.01
  </code></pre>
  
  <p>I am trying to get only the last row based on the first level of the multiindex, which is date in this case.</p>
  
  <pre><code>2013-01-01 a          -0.00
             b          -0.01
  </code></pre>
  
  <p>The first level index is datetime. What would be the most elegant way to select the last row?</p>