David and Marc, thank you very much for your quick and professional help.
Both approaches are doing what I was looking for. Next time I will try to provide an example that is more clearly. Regards, Stefan University of Bayreuth ______________________________________________ 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.
