Thanks for your reply, Frank. I've noticed that the x.knots object doesn't actually have to be the vector of knots. Just having x.knots <- 0 or even x.knots <- "a" will allow predict to work.
Mark Seeto Frank Harrell wrote: > > This is a consequence of predict.ols calling predictrms which relies on > model.frame which re-issues the expression of x.knots. You would have the > same problem if using update(fit object) in another session. For that > reason you have to keep an external knots vector available in your > environment. > > Frank > > > Mark Seeto wrote: >> >> Dear R-help, >> >> In the rms package, I have fitted an ols model with a variable >> represented as a restricted cubic spline, with the knot locations >> specified as a previously defined vector. When I save the model object >> and open it in another workspace which does not contain the vector of >> knot locations, I get an error message if I try to predict with that >> model. This also happens if only one workspace is used, but the vector >> of knot locations is removed: >> >> library(rms) >> set.seed(1) >> x <- rnorm(100) >> y <- 1 + x + x^2 + rnorm(100) >> >> x.knots <- quantile(x, c(0.2, 0.5, 0.8)) >> ols1 <- ols(y ~ rcs(x, x.knots)) >> >> predict(ols1, data.frame(x = 0)) # This works >> rm(x.knots) >> predict(ols1, data.frame(x = 0)) # Gives error >> >> The first predict gives >> 1 >> 0.8340293 >> >> while the second predict gives >> Error in rcs(x, x.knots) : object 'x.knots' not found >> >> The same error happens if x.knots is simply defined as a vector like >> c(-1, 0, 1) (i.e. not using quantile). Is this the intended behaviour? >> The requirement that x.knots be in the workspace seems strange, given >> that the knot locations are stored in ols1$Design$parms. >> >> Thanks for any help you can give. >> >> Mark Seeto >> National Acoustic Laboratories, Australia >> >> ______________________________________________ >> 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. >> > -- View this message in context: http://r.789695.n4.nabble.com/predict-with-model-rms-package-tp3581229p3583344.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.
