Try this: tapply(mydata$Correct, mydata$Subject, function(x)sum(x == "C"))
Sarah On Thu, Mar 24, 2011 at 3:24 PM, Kevin Burnham <kburn...@gmail.com> wrote: > I have a data file with indicates pretest scores for a linguistics > experiment. The data are in long form so for each of 33 subjects there are > 400 rows, one for each item on the test, and there is a column called > ‘Correct’ that shows ‘C’ for a correct response and ‘E’ for an incorrect > response. I am trying to write a formula that will create a vector that > indicates the number of correct answers for each subject. > > > > The following: > > > > nrow(pretestdata[(pretestdata$Subject=="1" & pretestdata$Correct=="C"),]) > > > > gives the number of correct responses for subject 1, but I would like a > vector that indicates the number correct for each of 33 subjects. > > > > Thank you sincerely for your assistance. > > > > Kevin Burnham > -- Sarah Goslee http://www.functionaldiversity.org ______________________________________________ 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.