title: I have to add two dataframes and calculate the sum for each account id
body: <p>df1</p>
  <pre><code>acc_id || s1_2005 || s1_2006
  87         1       1
  </code></pre>
  <p>df2</p>
  <pre><code>acc_id || s2_2005 || s2_2006
  87            2       3
  </code></pre>
  <p>output</p>
  <p>df3</p>
  <pre><code>acc_id ||s1_2005 + s2_2005 || s1_2006 + s2_2006
  87                3                   4
  </code></pre>