Mark, Henrique, and Jorge, Thank you all very much for your replies. I'm really impressed by your knowledge of R: I'd never even heard of of some of these functions (especially split() and unlist().)
I went with the Henrique-Mark solution and it is working fine. Thanks again! David [[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.