An alternative approach (clumsy but probably not as clumsy as a loop) would be to create a sixth column as a factor and aggregate on that. Simple-minded example : ======================================================= mydata <- data.frame(matrix(rnorm(100),nrow=20)) mydata[,6] <- c(rep("a",5),rep("b",20-10),rep("c",5)) aggregate(mydata[,5], by=list(mydata[,6]), mean)
============================================================ Set all the unwanted values to X and subset on that before calculating. --- On Sun, 12/27/09, Edouard Tallent <tallen...@lycos.com> wrote: > From: Edouard Tallent <tallen...@lycos.com> > Subject: [R] how to create a simple loop ? > To: r-help@r-project.org > Received: Sunday, December 27, 2009, 9:15 AM > Hi everyone. And, Merry Xmas ! > I have a 5-row matrix called “data”. There are > headers. > it look like this : > Row 1 Row2 Row3 > Row4 Row5 > Line1 … > … > … … > Line2 … > … > … … > Line3 … > … > … … > … > Line 1838 > … > … > … … > I want to calculate several simple arithmetic means for > Row5, that is from Line173 to Line193, from Line434 to > Line455, from Line699 to Line724, from Line955 to Line977 > A simple way is to individually compute these means. The > first one (Line173 to Line193) is then obtained by : > >mean(data[173:193,5], na.rm = TRUE) > That’s right ! But, I aim to automate this calculation by > creating a loop. > I tried many things, but I have been unsuccessful at using > the ‘for’ loop function. > Please, don’t explain things too hard as it is often the > case that people wants to help but gets into too much > sophistication. > Someone can write that little code for this example ? Or > suggest functions ? > Thanks for your help. > Cheers, > Édouard. > > [[alternative(swapped) HTML version > deleted]] > > This is MIME Epilogue > > > -----Inline Attachment Follows----- > > ______________________________________________ > 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. > __________________________________________________________________ Looking for the perfect gift? Give the gift of Flickr! http://www.flickr.com/gift/ ______________________________________________ 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.