title: Groupby sum and count on multiple columns in python
body: <p>I have a pandas dataframe that looks like this</p>
  
  <pre><code>ID     country   month   revenue  profit   ebit
  234    USA       201409   10        5       3
  344    USA       201409    9        7       2
  532    UK        201410    20       10      5
  129    Canada    201411    15       10      5
  </code></pre>
  
  <p>I want to group by ID, country, month and count the IDs per month and country and sum the revenue, profit, ebit.
  The output for the above data would be:</p>
  
  <pre><code> country   month    revenue   profit  ebit   count
     USA     201409     19        12      5      2
     UK      201409     20        10      5      1
     Canada  201411     15        10      5      1
  </code></pre>
  
  <p>I have tried different variations of groupby, sum and count functions of pandas but I am unable to figure out how to apply groupby sum and count all together to give the result as shown. Please share any ideas that you might have. Thanks! </p>