cast in reshape and reshape2
Have you looked at the .summarise argument to dcast? That seems to deliver the same sort of results one gets with base::aggregate.
Actually I see after looking at examples on the plyr-reshape-googlegroups group that it is not '.summarise' but rather 'summarise'. Unfortunately there are no links in the help pages that seem to describe its proper use ... a not uncommon failing for that package in my experience.
?plyr::summarise seems pretty helpful to me. If you can do better, please submit a patch - they are very much appreciated. Hadley
Assistant Professor / Dobelman Family Junior Chair Department of Statistics / Rice University http://had.co.nz/