Hi Jason, If I understand correctly, you are looking for something along the lines of
with(X, tapply(author, articleID, function(x) length(unique(x)))) # 1 2 3 # 1 2 2 with X your data frame. HTH, Jorge On Sun, Nov 1, 2009 at 1:20 AM, Jason Priem <> wrote: > I've got a data frame describing comments on an electronic journal, wherein > each row is a unique comment, like so: > > commentID author articleID > 1 1 smith 2 > 2 2 jones 3 > 3 3 andrews 2 > 4 4 jones 1 > 5 5 johnson 3 > 6 6 smith 2 > > I want know the number of unique authors per article. I can get a table of > article frequencies with table(articleID), but I can't figure out how to > count frequencies in a different column. I'm sure there's an easy way, but > I guess I'm too new at this to find it. Thanks for your help! > > Jason Priem > PhD student, School of Information and Library Science, University of North > Carolina-Chapel Hill > > ______________________________________________ > 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. > [[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.
