title: How do I calculate a new column in Pandas based a on trignometric function?
body: <p>I have a dataframe with the following columns (sin and cos of a angle)</p>
  
  <pre><code>                SWD         CWD
  2013-12-06  -0.394097   -0.350099
  2013-12-07  -0.388295   -0.271105
  2013-12-08  -0.391894   -0.202537
  2013-12-09  -0.388662   -0.430063
  2013-12-10  -0.396427   -0.433933
  </code></pre>
  
  <p>How can I create a new column with the arctan of the angle (atan(sin/cos)?</p>
  
  <p>Thank you</p>
  
  <p>Hugo</p>