Hello, I believe that
by( data.ex, data.ex[,c(3,4)], function(x) x[which.max(x[,1]),] ) does what you want. Then, do.call( rbind, by( data.ex, data.ex[,c(3,4)], function(x) x[which.max(x[,1]),] ) ) looks somewhat nicer. Best regards, Carlos J. Gil Bellosta http://www.datanalytics.com On Fri, 2009-07-24 at 13:06 -0400, Afshartous, David wrote: > All, > > For data consisting of serial measurements on subjects, one may use the > aggregate function to say compute the peak response for each subject for > each design condition. Is there a way to alter this or another one-liner to > also retain the time at which the peak occurred and thus avoid writing a > doing this via a loop? I suppose one could attempt to employ the split > function but that's probably no simpler than employing a loop. Sample code > below: > > > data = expand.grid(time = seq(1,6), subject = seq(1,20), treatment = > c("placebo", "drug")) > data.ex = cbind(y = rnorm(dim(data)[1], 5, 1), data.ex) > > data.peak = aggregate(data.ex[c(1)], data.ex[c(3,4)], max) > ## this provides the peak of each subject on each treatment, but time is > ## lost. Including time in the statement doesn't help clearly as then > ## the peak of all the times will be calculated > > > David > > -------------------------------------- > David Afshartous, Ph.D. > Research Assistant Professor > University of Miami, Miller School of Medicine > Division of Clinical Pharmacology > 1500 N.W. 12th Avenue, 15th Floor West > Miami, Florida 33136 > > E-mail: afs...@med.miami.edu > Phone: +1 305-243-1549 > > ______________________________________________ > 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.
