title: R zoo series sliding window calculation
body: <p>Given I have a zoo dataset, I'd like to perform a sliding operation against it with the result being another zoo dataset.</p>
  
  <pre>
  > x
                        Y
  (09/24/09 08:00:13)   3.1
  (09/24/09 08:05:13)   4.2
  (09/24/09 08:10:13)   4.5
  (09/24/09 08:15:13)   9.4
  (09/24/09 08:20:13)   9.8
  (09/24/09 08:25:13)   7.7
  (09/24/09 08:30:13)  13.3
  (09/24/09 08:35:13)   6.5
  (09/24/09 08:40:13)  14.7
  (09/24/09 08:45:13)  23.5
  (09/24/09 08:50:13)  20.9
  (09/24/09 08:55:13)   8.5
  </pre>
  
  <p>My goal is to produce a "smooth" average by iterating through each time interval and obtaining the mean for the set of Y points that are +/- 15 minutes of the current point.</p>
  
  <p>I have a bucketing method of averaging working, but it reduces the resolution of the data. I haven't worked out how to make relative subsets out of zoo with artibrary math, window should help but accessing the index is being difficult.</p>
  
  <p>Thanks.</p>