title: How can I calculate cumulative percentage change from beginning period
body: <p>I am trying to create a <code>DataFrame</code> with a rolling cumulative percentage change. I would like to show the percentage change of the stock from the initial buy date (2014-09-05).</p>
  
  <pre><code>import pandas as pd
  import pandas.io.data as web
  
  cvs = web.get_data_yahoo('cvs', '2014-09-05')['Adj Close']
  
  cvsChange = cvs[1:] / cvs.shift(1) - 1
  </code></pre>