title: Pandas: sum values two columns consisting of lists
body: <p>I have a Pandas dataframe looking like this.</p>
  
  <pre><code>id       discount          current_price
  01188    [0, 0, 0, 78]     [0, 294, 294, 294, 294, 294, 294, 294, 294, 294]
  </code></pre>
  
  <p>The column <code>discount</code> and <code>price</code> are both consist of a list of integers. I would like to create a new column called <code>old_price</code> with the sum of <code>discount</code> and <code>price</code> element-wise.</p>
  
  <p>So the new column would have:
  <code>[0, 294, 294, 372, 294, 294, 294, 294, 294, 294]</code></p>