Adaikalavan, thanks for your phantastic summary. Solution 5 is the version I was looking for, but I left out the cbind in good old c-fashion.
> # Solution 5 : Vectorised operation with list extractor > system.time( ee <- PatDay$Day - StartDay[ cbind(PatDay$Treat,PatDay$Pat) Dieter ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
