Here's one way, lapply(split(DF, your.vector), function(x) {apply(x, 2, sum)})
> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Daniel O'Shea > Sent: Tuesday, August 21, 2007 3:53 PM > To: r-help@stat.math.ethz.ch > Subject: [R] summing columns of data frame by group > > I have a data frame and one separate vector that is a > grouping variable for the data frame. I would like to take > all rows of the data frame belonging to each group and then > sum the columns with out using a for statement. > > Something like: take all rows of group 1 then > apply(group1.data,1,sum), but do this without having to do it > separately for each group. Any ideas? thank you. > > Dan > > ______________________________________________ > 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 > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ 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 and provide commented, minimal, self-contained, reproducible code.