Thanks, that is much faster. I don't quite understand it, but that's OK for now.
Thanks again, Matthew On Sat, Feb 25, 2012 at 9:00 PM, Matthew Dowle <[email protected]>wrote: > Hi. There have been thoughts of adding .I for that. In the meantime > something like this should be faster: > DT[DT[,X1==max(X1),by='x,y,z'][[4]]] > > > I know that we shouldn't subset .SD, but I would like to return the row > > from each group that corresponds to a max value in one of the columns. > > Here's how I'm doing it currently: > > > > maxrows<- df.dt[, .SD[which(X1== max(X1)),], by = list(Var1, Var2, Var3)] > > > > Is there a better way? > > > > Thank you kindly, > > > > Matthew > > _______________________________________________ > > datatable-help mailing list > > [email protected] > > > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help > > >
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