title: Pandas multiindex dataframe - Selecting max from one index within multiindex
body: <p>I've got a dataframe with a multi index of Year and Month like the following</p>
  
  <pre><code>     |     |Value
  Year |Month|  
       |  1  |  3
  1992 |  2  |  5
       |  3  |  8
       | ... | ...
  1993 |  1  |  2
       | ... | ...
  </code></pre>
  
  <p>I'm trying to select the maximum Value for each year and put that in a DF like this: </p>
  
  <pre><code>     | Max
  Year |  
  1992 |  5
  1993 |  2
       | ... 
  </code></pre>
  
  <p>There's not much info on multi-indexes, should I simply do a group by and apply or something similar to make it more simple?</p>