title: How to ddply() without sorting?
body: <p>I use the following code to summarize my data, grouped by Compound, Replicate and Mass.</p>
  
  <pre><code>summaryDataFrame &lt;- ddply(reviewDataFrame, .(Compound, Replicate, Mass), 
    .fun = calculate_T60_Over_T0_Ratio)
  </code></pre>
  
  <p>An unfortunate side effect is that the resulting data frame is sorted by those fields. I would like to do this and keep Compound, Replicate and Mass in the same order as in the original data frame. Any ideas? I tried adding a "Sorting" column of sequential integers to the original data, but of course I can't include that in the .variables since I don't want to 'group by' that, and so it is not returned in the summaryDataFrame.</p>
  
  <p>Thanks for the help.</p>