title: Pandas: Cumulative return function
body: <p>I have a dataframe such as the following:</p>
  
  <pre><code>  Index      Return
  2008-11-21   0.153419
  2008-11-24   0.037421
  2008-11-25   0.077500
  </code></pre>
  
  <p>What's the best way to calculate a cumulative return across all columns on the last row?</p>
  
  <p>Following is the intended result:</p>
  
  <pre><code>  Index      Return
  2008-11-21   0.153419
  2008-11-24   0.037421
  2008-11-25   0.077500
  Cumulative   0.289316
  </code></pre>
  
  <p>Where cumulative return calculated as follows:</p>
  
  <pre><code>cumulative = (1 + return1) * (1 + return2) * (1 + return3) - 1 
  </code></pre>
  
  <p>What is the best way to perform this in pandas?</p>