Comparison with R should discuss dcast as well as aggregate
The [Comparison with R](http://pandas.pydata.org/pandas-docs/stable/comparison_with_r.html) docs have a great section on how to go from R's `aggregate` function to Pandas's `groupby`, but as [this StackOverflow](http://stackoverflow.com/questions/25043927/dcast-replicate-in-python) question shows, there are similar but not identical problems going from R's `dcast` to Panda's `groupby` and `aggregate`.

I'm not sure exactly what the documentation should say here. (By the way, I'm also by no means sure that my answer to that question was the best one, so feel free to chime in there too…), just that maybe it should say _something_.
