title: Calculating Rolling forward averages with pandas
body: <p>I need to calculate some rolling forward averages in a dataframe and really don't know where to start.</p>
  
  <p>I know if I wanted to select a cell 10 days ahead say I would do <code>df.shift(-10)</code>, but what I'm looking to do is calculate the average between 10 and 15 days ahead say.</p>
  
  <p>So what I'm kind of thinking is <code>df.rolling(-10,-15).mean()</code>, if I was trying to calculate just a moving average going backing in time df.rolling(15, 10).mean() would work perfectly and I did think about just calculating the averages like that, and then somehow shifting the data.</p>
  
  <p>Any help would be great</p>
  
  <p>Many thanks</p>