title: R - Changing XTS Periodicity Subsetted By Variable
body: <p>I currently have an xts with a character string column called "Symbol" and then several columns of numerical and character data. The data is mostly weekly and also at the end of the month. I would like to aggregate this data to a monthly periodicity for each of the "Symbols" present in the data, so in other words I want to get the monthly data for each symbol, not just for a random symbol which is chosen by quantmod. I tried using </p>
  
  <pre><code>to.period(df.xts, 'years', OHLC = FALSE)
  </code></pre>
  
  <p>from <code>quantmod</code> but ran into the problem that only one row was being chosen for each month.</p>