You have three levels of factor 'ippo' and data on two. That is not a two-sample problem, as the error message says. Try
IPPOBIS$ippo <- IPPOBIS$ippo[drop=TRUE] And please use an informative subject line (see the posting guide). On Thu, 12 Jul 2007, Cressoni, Massimo (NIH/NHLBI) [F] wrote: > I need to perform the Exact Wilcoxon Mann-Whitney on a subset of my database. > Assuming that IPPO is my data frame and IPPOBIS is the subset my variable > still > have 3 different levels and the function wilcox_test (package "coin") > does not accept it. > I do not know how to overcome this problem. > > ippo <- c(rep("A",10),rep("B",10),rep("C",10)) > ippo2 <- c(rnorm(10,0,1),rnorm(10,10,10),rnorm(10,10,10)) > IPPO <- data.frame(ippo,ippo2) > > IPPOBIS <- IPPO[IPPO$ippo == "A" | IPPO$ippo == "B",] > > wilcox_test(ippo2 ~ ippo,data=IPPOBIS,distribution=exact()) > Error in check(itp) : 'object' does not represent a two sample problem > levels(IPPOBIS$ippo) > [1] "A" "B" "C" > > Massimo Cressoni > > ______________________________________________ > R-help@stat.math.ethz.ch 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. > -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-help@stat.math.ethz.ch 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.