Thanks for your help Petr I think I understand better now.
> > > Masechaba$unique[which(is.na(unique(Masechaba$PROPDESC))==FALSE)]=TRUE > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > This seems to be strange. At first sight I am puzzlet what result I shall > expect from such construction. > > About your comment above: I looked at the construction again. This was absolutely unsuited to what I actually had in mind and based on a wrong understanding of how unique() functions. When one uses is.na(unique(x)) the answer is FALSE as long a there is something unique - which there will always be as long as there are any values. It therefore produces a list of FALSE the same length as the result of unique. which() gives the indices namely 1:length(unique(x)) The desired result (a true or false value indicating whether a variable is a duplicate or not is obtained by Masechaba$unique=duplicated(match(Masechaba$PROPDESC,unique(Masechaba$PROPDESC))) Thanks again for your help regards Christiaan [[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.