title: pandas rolling sum of last five minutes
body: <p>Assume I have below data frame</p>
  
  <pre><code>Date, A
  2014-11-21 11:00:00, 1
  2014-11-21 11:03:00, 4
  2014-11-21 11:04:00, 1
  2014-11-21 11:05:00, 2
  2014-11-21 11:07:00, 4
  2014-11-21 11:08:00, 1
  2014-11-21 11:12:00, 1
  2014-11-21 11:13:00, 2
  </code></pre>
  
  <p>First column is datetime object and second column is an integer. What I want is to calculate the sum of column 'A' for the last five minute for each row. </p>
  
  <p>As an example for the row  <code>2014-11-21 11:12:00, 1</code>, the sum of column 'A' would be 2(1+1) and the sum of column 'A' for the row <code>2014-11-21 11:05:00, 2</code> would be 7(2+1+4). Important thing is that the number of past rows for the time window(5 minutes) is not the same for each row (Because time series is irregular).</p>
  
  <p>How can I get the sum of last five minutes for column 'A' using the rolling_sum method in pandas? Thanks in advance.</p>