You might want to look at package plyr and use ddply. HTH,
Nick Sabbe -- ping: nick.sa...@ugent.be link: http://biomath.ugent.be wink: A1.056, Coupure Links 653, 9000 Gent ring: 09/264.59.36 -- Do Not Disapprove > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of Marius Hofert > Sent: woensdag 17 augustus 2011 12:42 > To: Help R > Subject: [R] How to apply a function to subsets of a data frame *and* > obtain a data frame again? > > Dear all, > > First, let's create some data to play around: > > set.seed(1) > (df <- data.frame(Group=rep(c("Group1","Group2","Group3"), each=10), > Value=c(rexp(10, 1), rexp(10, 4), rexp(10, > 10)))[sample(1:30,30),]) > > ## Now we need the empirical distribution function: > edf <- function(x) ecdf(x)(x) # empirical distribution function > evaluated at x > > ## The big question is how one can apply the empirical distribution > function to > ## each subset of df determined by "Group", so how to apply it to > Group1, then > ## to Group2, and finally to Group3. You might suggest (?) to use > tapply: > > (edf. <- tapply(df$Value, df$Group, FUN=edf)) > > ## That's correct. But typically, one would like to obtain not only the > values, > ## but a data.frame containing the original information and the new > (edf-)values. > ## What's a simple way to get this? (one would be required to first > sort df > ## according to Group, then paste the values computed by edf to the > sorted df; > ## seems a bit tedious). > ## A solution I have is the following (but I would like to know if > there is a > ## simpler one): > > (edf.. <- do.call("rbind", lapply(unique(df$Group), function(strg){ > subdata <- subset(df, Group==strg) # sub-data > subdata <- cbind(subdata, edf=edf(subdata$Value)) > })) ) > > > Cheers, > > Marius > ______________________________________________ > 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.
