title: Pandas group by and sum two columns
body: <p>Beginner question. This seems like it should be a straightforward operation, but I can't figure it out from reading the docs.</p>
  
  <p>I have a df with this structure:  </p>
  
  <pre><code>|integer_id|int_field_1|int_field_2|
  </code></pre>
  
  <p>The integer_id column is non-unique, so I'd like to group the df by integer_id and sum the two fields.</p>
  
  <p>The equivalent SQL is:</p>
  
  <pre><code>SELECT integer_id, SUM(int_field_1), SUM(int_field_2) FROM tbl
  GROUP BY integer_id
  </code></pre>
  
  <p>Any suggestions on the simplest way to do this?</p>
  
  <p>EDIT: Including input/output  </p>
  
  <pre><code>Input:  
  integer_id  int_field_1 int_field_2   
  2656        36          36  
  2656        36          36  
  9702        2           2  
  9702        1           1  
  </code></pre>
  
  <p>Ouput using df.groupby('integer_id').sum():  </p>
  
  <pre><code>integer_id  int_field_1 int_field_2  
  2656        72          72  
  9702        3           3  
  </code></pre>