title: How do I calculate a monthly rate of change from a daily time series in R?
body: <p>I'm beginning to get my feet wet with R, and I'm brand new to time series concepts. Can anyone point me in the right direction to calculate a monthly % change, based on a daily data point? I want the change between the first and last data points of each month. For example:</p>
  
  <p>tseries data:</p>
  
  <pre><code>1/1/2000 10.00
  ...
  1/31/2000 10.10
  2/1/2000 10.20
  ...
  2/28/2000 11.00
  </code></pre>
  
  <p>I'm looking for a return data frame of the form:</p>
  
  <pre><code>1/31/2000 .01
  2/28/2000 .0784
  </code></pre>
  
  <p>Ideally, I'd be able to calculate from the endpoint of the prior month to the endpoint of current month, but I'm supposing partitioning by month is easier as a starting point. I'm looking at packages zoo and xts, but am still stuck. Any takers? Thanks...</p>