stephen, Thanks for your help. I want to draw a plot which shows separate survival curves for each category of X on the same plot(same set of axes). Your code produces a separate curve for each combination of X and Y but I don't want curves for combinations of X and Y since Y has many levels and also the values of Y don't have any significance in my case. Is there a way of doing what i want to do i.e. getting separate survival curves for each level of X using the function survfit() on an object mod.phm which is a coxph object such that:
mod.phm<-coxph(formula=Surv(time,Flag_Death)~X+Y, data= datFrame) Help On Nov 14, 2007 9:08 AM, Stephen Weigand <[EMAIL PROTECTED]> wrote: > On Nov 13, 2007 5:53 AM, Shoaaib Mehmood <[EMAIL PROTECTED]> wrote: > > > i want to make survival plots for a coxph object using survfit > > function. mod.phm is an object of coxph class which calculated results > > using columns X and Y from the DataFrame. Both X and Y are > > categorical. I want survival plots which shows a single line for each > > of the categories of X i.e. '4' and 'C'. I am getting the following > > error: > > > > > attach(DataFrame) > > > DataFrame.X<-data.frame(X=c('4','C'),Y=rep(mean(Y),2)) > > > detach() > > As you have it, Y in DataFrame.X will be created as numeric > which isn't what you probably want (since you say Y is > categorical). > > Also, you will run into problems if you create newdata and it > doesn't have all the levels of all the factors in your model. You > can do this: > > newdat <- expand.grid(X = c("4", "C", plus all other levels), > Y = c("2", plus all other levels)) > > plot(survfit(cox.mod, newdata = subset(newdat, Y == "2"))) > > > > > plot(survfit(mod.phm, newdata=DataFrame.X), lty=c(1,2),ylim=c(.6,1)) > > Error in `contrasts<-`(`*tmp*`, value = "contr.treatment") : > > contrasts can be applied only to factors with 2 or more levels > > > > any help will be appreciated. > > > -- Regards, Rana Shoaaib Mehmood ______________________________________________ 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.