Hi all: My data:data(sleep) If I wanna calculate each group's extra,what I can do is: #method1 attach(sleep) mean(extra[group==1]) mean(extra[group==1])
#method2 result<-matrix(,0,2) g<-split(sleep,sleep$group) for(i in 1:length(g)) { result<-rbind(result,data.frame(unique(g[[i]]$group),mean(g[[i]]$extra))) } colnames(result)<-c("name","mean") But the above 2 method is a little bit tedious.Is there a "short cut" manner to get the same result? Thanks a lot! My best [[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.