I spent a while chasing this one down! In S S> unique(NULL) NULL whereas in R (both 0.61.1 and yesterday's 0.62-snapshot) > unique(NULL) Error: duplicated applies only to vectors I think I prefer the behaviour in S. Although there is code in the do_duplicated function in $RHOME/src/main/unique.c to handle the case of zero-length vectors it appears that the check for isVector(x) immediately before that is what is causing the problem. Would it be as simple as changing the check on if (!isVector(x)) to if (!(isVector(x) || isNull(x))) -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-devel-request@stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._