title: Aggregate Daily Data to Month/Year intervals
body: <p>I don't often have to work with dates in R, but I imagine this is fairly easy.  I have a column that represents a date in a dataframe.  I simply want to create a new dataframe that summarizes a 2nd column by Month/Year using the date.  What is the best approach?</p>
  
  <p>I want a second dataframe so I can feed it to a plot.</p>
  
  <p>Any help you can provide will be greatly appreciated!</p>
  
  <p>EDIT:  For reference:</p>
  
  <pre><code>&gt; str(temp)
  'data.frame':   215746 obs. of  2 variables:
   $ date  : POSIXct, format: "2011-02-01" "2011-02-01" "2011-02-01" ...
   $ amount: num  1.67 83.55 24.4 21.99 98.88 ...
  
  &gt; head(temp)
          date amount
  1 2011-02-01  1.670
  2 2011-02-01 83.550
  3 2011-02-01 24.400
  4 2011-02-01 21.990
  5 2011-02-03 98.882
  6 2011-02-03 24.900
  </code></pre>