P=data.frame(x=c(1,1,2,3,2,1),y=rnorm(6)) tapply(P$y,P$x,sum)
regards, stefan On Mon, Nov 16, 2009 at 09:49:17AM -0800, Gunadi wrote: > > I am sure this is easy but I am not finding a function to do this. > > I have two columns in a matrix. The first column contains multiple entries > of numbers from 1 to 100 (i.e. 10 ones, 8 twos etc.). The second column > contains unique numbers. I want to sum the numbers in column two based on > the indexed values in column one (e.g. sum of all values in column two > associated with the value 1 in column one). I would like two columns in > return - the indexed value in column one (i.e. this time no duplicates) and > the sum in column two. > > How do I do this? > -- > View this message in context: > http://old.nabble.com/Sum-over-indexed-value-tp26376359p26376359.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help@r-project.org 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@r-project.org 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.