Hi all, and thank you for your interested answers. The problem could be already solved. It is present on my old R 2.15.1 (x86_64-pc-linux-gnu), but after reproducing the error I got the expected result on a R 3.0.2 through a web interface. However, since I spent a considerable amount of time to understand what was happening, I nevertheless decided to submit to your attention what i found.
The following code reproduces the problem on my system (and probably on every Debian 7 "Wheezy" system with no cran repositories added) library(survival) library(rms) Hazards <- rep(c(1/3, 1/10), each=50) FupTimes <- rexp(100, rate=Hazards) CensTimes <- rexp(100, rate=Hazards) # just for fun, we don't need censoring here Status <- ifelse(FupTimes <= CensTimes, 1, 0) FupTimes <- ifelse(Status==1, FupTimes, CensTimes) SurvObj <- Surv(FupTimes, Status) # let's manually order the levels: Covariate <- factor(rep(c("A","B"), each=50), labels=c("B", "A")) SurvfitObj <- survfit(SurvObj ~ Covariate) survplot(SurvfitObj, conf="none", n.risk=TRUE, levels.only=TRUE, time.inc=1) (Resulting plot has nrisk labels inverted) The error was much simpler than I initially thought, and it is actually unrelated to survfit. I think that survplot relies (on my R) on the factor's levels being alphabetically ordered with the underlying numerical code appropriately arranged (which I believe is the default behavior of factor() ). There is no problem if the covariate is a character vector, since in that case the survfit$strata names have the expected order. Incidentally, debugging this little problem, I also found that if the internal nrisk vector has length 1 the survplot function gives error (line 244 in my version), and this is why I put time.inc=1 in the previous call (This other issue is still present in 3.0.2) I'm going to upgrade my R and check that this little error is actually gone. Thank you Marco 2014-07-03 0:17 GMT+02:00 Frank Harrell <f.harr...@vanderbilt.edu>: > Please try hard to create a simple reproducible example, then I'll work > on it. > > > > [[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. ______________________________________________ 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.