HI, Try this: dat1 <- read.table(text=" subject time.ms V3 1 1 stringA 1 12 stringB 1 22 stringC 2 1 stringB 2 14 stringC 2 25 stringA ", sep="",header=TRUE) dat2<-aggregate(dat1$time.ms,list(dat1$subject),max) colnames(dat2)<-c("subject","time.ms")
merge(dat2,dat1) subject time.ms V3 1 1 22 stringC 2 2 25 stringA A.K. ----- Original Message ----- From: Miriam <miriam_kathar...@gmx.de> To: r-help@r-project.org Cc: Sent: Tuesday, June 26, 2012 5:21 PM Subject: [R] selecting rows by maximum value of one variables in dataframe nested by another Variable How could I select the rows of a dataset that have the maximum value in one variable and to do this nested in another variable. It is a dataframe in long format with repeated measures per subject. I was not successful using aggregate, because one of the columns has character values (and/or possibly because of another reason). I would like to transfer something like this: subject time.ms V3 1 1 stringA 1 12 stringB 1 22 stringC 2 1 stringB 2 14 stringC 2 25 stringA …. To something like this: subject time.ms V3 1 22 stringC 2 25 stringA … Thank you very much for you help! Miriam -- Jetzt informieren: http://mobile.1und1.de/?ac=OM.PW.PW003K20328T7073a ______________________________________________ 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.