On Wed, Jan 26, 2011 at 5:27 AM, Dennis Murphy <djmu...@gmail.com> wrote: > Hi: > > Here are two more candidates, using the plyr and data.table packages: > > library(plyr) > ddply(X, .(x, y), function(d) length(unique(d$z))) > x y V1 > 1 1 1 2 > 2 1 2 2 > 3 2 3 2 > 4 2 4 2 > 5 3 5 2 > 6 3 6 2 > > The function counts the number of unique z values in each sub-data frame > with the same x and y values. The argument d in the anonymous function is a > data frame object.
Another approach is to use the much faster count function: count(unique(X)) Hadley -- Assistant Professor / Dobelman Family Junior Chair Department of Statistics / Rice University http://had.co.nz/ ______________________________________________ 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.
