split the data frame, cbind the count and unsplit back: DF <- data.frame(A = c("A", "A", "A", "B", "C"), B = c(1, 1, 2, 2, 0))
> g <- paste(DF$A, DF$B) > s <- split(DF, g) > u <- lapply(s, function(x) cbind(x, Occurs = nrow(x))) > unsplit(u, g) A B Occurs 1 A 1 2 2 A 1 2 3 A 2 1 4 B 2 1 5 C 0 1 See ?split where there is a very similar example. On Dec 9, 2007 4:35 AM, christopher snow <[EMAIL PROTECTED]> wrote: > I have a table with two columns: > > A 1 > A 1 > A 2 > B 2 > C 0 > > I would like to produce a third column that contains the counts of each > unique combination of col1 and col2: > > A 1 2 > A 1 2 > A 2 1 > B 2 1 > C 0 1 > > How can I do this in R? > > Thanks in advance ... > > > -- > This message has been scanned for viruses and > dangerous content by MailScanner, and is > believed to be clean. > > ______________________________________________ > 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.