The most common would be aggregate. You can change mean for other functions ( e.g. sum or length, median, or one you write yourself)
You probably would find Bob Munechen's book http://rforsasandspssusers.com/ very useful and there is a shorter pdf available on that page. Example: dd <- data.frame(factor1= rep(letters[1:10], 2), factor2=rep(LETTERS[1:5],4), var1=rnorm(20, 10,2), var2=rnorm(20, 25,5)) aggregate(dd[,3:4], by=list(dd[,1],dd[,2]), mean) aggregate(dd[,3:4], by=list(dd[,1],dd[,2]), sum) --- On Thu, 7/30/09, Pat Schmitz <p.schm...@gmail.com> wrote: > From: Pat Schmitz <p.schm...@gmail.com> > Subject: [R] What is the best method to produce means by categorical factors? > To: r-help@r-project.org > Received: Thursday, July 30, 2009, 4:19 AM > I am attempting to replicate some of > my experience from SAS in R and assume > there are best methods for using a combination of > summary(), subset, and > which() to produce a subset of mean values by categorical > or ordinal > factors. > > within sas I would write > > proc means mean data=dataset; > class factor1 factor2 > var variable1 variable2; > RUN; > > producing an output with means for each variable by factor > groupings as > below: > > *factor1 factor2 > obs > variable mean* > Level A treatmentA > 3 variable1 > 10 > > > variable2 > 22 > > > treatmentB > 3 variable1 12 > > > variable2 > 30 > > Level B treatmentA > 3 variable1 > 10 > > > variable2 > 22 > > > treatmentB > 3 variable1 12 > > > variable2 > 30 > > What is the best way to go about this in R? > > > > > > > -- > Patrick Schmitz > Graduate Student > Plant Biology > 1206 West Gregory Drive > RM 1500 > > [[alternative HTML version deleted]] > > ______________________________________________ > 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. > __________________________________________________________________ Yahoo! Canada Toolbar: Search from anywhere on the web, and bookmark your favourite sites. Download it now http://ca.toolbar.yahoo.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.
