This does work: coxph(survobj~group, data=df.test[[1]]) # this works like your original
To get insight compare: str(survobj) str(df.test) str(df.test[[1]]) Then note the 2nd sentence of the following from ?coxph Arguments: formula: a formula object, with the response on the left of a '~' operator, and the terms on the right. The response must be a survival object as returned by the 'Surv' function. ____________________________ Robert W. Baer, Ph.D. Associate Professor Department of Physiology A. T. Still University of Health Science 800 W. Jefferson St. Kirksville, MO 63501-1497 USA Dear All, a Surv object I put in a data frame behaves somehow unexpected (see example). If I do a Cox regression on the original Surv object it works. If I put it in a data.frame and do the regression on the data frame it does not work. Seemingly it has to do with the class attribute, because if I change the class attribute to let "Surv" appeare first, again it works. Is this known? Should I have found information on it? Any comments? Thanks Heinz Tüchler ## example data starttime <- rep(0,5) stoptime <- 1:5 event <- c(1,0,1,1,1) group <- c(1,1,1,2,2) ## Surv object survobj <- Surv(starttime, stoptime, event) ## Cox-regression coxph(survobj~group) # this works ## put Surv object in data.frame df.test <- data.frame(survobj=I(survobj), group) ## Cox-regression on data.frame coxph(survobj~group, data=df.test) # this does not work attr(df.test$survobj, 'class') # survobject has class "AsIs", "Surv" attr(df.test$survobj, 'class') <- c('Surv', 'AsIs') # put Surv first attr(df.test$survobj, 'class') # survobject has class "Surv", "AsIs" coxph(survobj~group, data=df.test) # now it works ______________________________________________ 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 ______________________________________________ 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