Hi Simon, Is this what you want?
mydat$cum.news<-unlist(tapply(mydat$news,mydat$state,FUN=cumsum)) Weidong Gu On Sat, Jul 23, 2011 at 7:11 AM, Simon Kiss <sjk...@gmail.com> wrote: > Dear colleagues, I have a data set that looks roughly like this; > mydat<-data.frame(state=c(rep("Alabama", 5), rep("Delaware", 5), > rep("California", 5)), news=runif(15, min=0, max=8), cum.news=rep(0, 15)) > > For each state, I'd like to cumulatively sum the value of "news" and make > that put that value in cum.news. > > I'm trying as follows but I get really weird results. One thing is that it > keeps counting 0's as 1. > > for (i in levels(mydat$state)) { > mydat[mydat$state==i, ]$cum.news<-sapply(mydat[mydat$state==i, ]$news, > function(x) sum(1:x)) > } > > I can sort of get the same sapply function to do what I want when working on > a test string > test<-1:10 > sapply(test, function(x) sum(1:x)) > > Any thoughts? > Simon Kiss > ********************************* > Simon J. Kiss, PhD > Assistant Professor, Wilfrid Laurier University > 73 George Street > Brantford, Ontario, Canada > N3T 2C9 > Cell: +1 905 746 7606 > > ______________________________________________ > 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.