title: Pandas. Group by index and apply max for column
body: <p>I am trying to group dataframe by 3 elements and want to get rows with the highest column value from the group, but <code>max</code> method applies to all columns. How can I achieve this?</p>
  
  <p>What I do:</p>
  
  <pre><code>In [69]: fr
  Out[69]:
               ping  delta
  0   1516190798773    161
  1   1516191845372    143
  2   1516192904988    144
  
  3   1516193952748    295
  4   1516195008033    233
  5   1516196049407    252
  
  In [70]: fr.groupby(fr.index / 3).max()
  Out[70]:
              ping  delta
  0  1516192904988    161
  1  1516196049407    295
  </code></pre>
  
  <p>Result I want to get:</p>
  
  <pre><code>            ping  delta
  0  1516190798773    161
  1  1516193952748    295
  </code></pre>