Hi not sure about speed but aggregate can probably do it.
aggregate(x, list(groupvec), sum, na.rm=T) HTH Petr On 12 May 2006 at 11:48, Werner Wernersen wrote: Date sent: Fri, 12 May 2006 11:48:45 +0200 (CEST) From: Werner Wernersen <[EMAIL PROTECTED]> To: r-help@stat.math.ethz.ch Subject: [R] optimal way to compute matrix subtotals? > Hi! > > I have large matrices, one column per variable and I have a vector of > factors / grouping symbols. Then I am computing subtotals for the > groups but it takes pretty long and thus I wanted to ask if there is a > better way to do it or if this is already the best way: subTotals <- > function(x, groupvec) > do.call("rbind",lapply(split(x,groupvec),colSums,na.rm=T)) > > > Thanks reading my question and any hints! > Werner > > > --------------------------------- > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html Petr Pikal [EMAIL PROTECTED] ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html