Hi, On Wed, Nov 11, 2009 at 8:51 PM, zwarren <zack.war...@yahoo.com> wrote: > > Hello! > > I'm trying to runs stats on two vars at a time in a big data frame. I knew > how to do this in SAS many years ago, but have half-forgotten that as well! > > I need, for instance, mean(value) by x-y combination: > x y z value > 1 1 1 10 > 1 1 2 20 > 1 2 1 30 > > with results: > x y mean(value) > 1 1 15 > 1 2 30
What happend to your "z" column? Anyway, there are a few ways you can do this. 1. If you just want to use the standard library, try the aggregate function. Roghly: R> df <- data.frame(x=c(1,1,1), y=c(1,1,2), z=c(1,2,1), value=c(10,20,30)) R> aggregate(df, by=list(df$x, df$y), mean) Group.1 Group.2 x y z value 1 1 1 1 1 1.5 15 2 1 2 1 2 1.0 30 2. You can try using the plyr library: R> library(plyr) R> ddply(df, .(x, y), mean) x y z value 1 1 1 1.5 15 2 1 2 1.0 30 HTH, -steve -- Steve Lianoglou Graduate Student: Computational Systems Biology | Memorial Sloan-Kettering Cancer Center | Weill Medical College of Cornell University Contact Info: http://cbio.mskcc.org/~lianos/contact ______________________________________________ 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.
