[R] test logistic regression model

[Bert Gunter]

small reprex:

set.seed(5)
dat <- data.frame(f = rep(c('r','g'),4), y = runif(8))
newdat <- data.frame(f =rep(c('r','g','b'),2))
## convert values in newdat not seen in dat to NA
is.na(newdat$f) <-!( newdat$f %in% dat$f)
lmfit <- lm(y~f, data = dat)

##Result:
> predict(lmfit,newdat)
        1         2         3         4         5         6
0.4374251 0.6196527        NA 0.4374251 0.6196527        NA

If this does not suffice, as Rui said, we need details of what you did.
(predict.glm works like predict.lm)


-- Bert


On Sun, Nov 20, 2022 at 7:46 AM Rui Barradas <ruipbarradas using sapo.pt> wrote:
>
> Às 15:29 de 20/11/2022, Gábor Malomsoki escreveu:
> > Dear Bert,
> >
> > Yes, was trying to fill the not existing categories with NAs, but the
> > suggested solutions in stackoverflow.com unfortunately did not work.
> >
> > Best regards
> > Gabor
> >
> >
> > Bert Gunter <bgunter.4567 using gmail.com> schrieb am So., 20. Nov. 2022, 16:20:
> >
> >> You can't predict results for categories that you've not seen before
> >> (think about it). You will need to remove those cases from your test set
> >> (or convert them to NA and predict them as NA).
> >>
> >> -- Bert
> >>
> >> On Sun, Nov 20, 2022 at 7:02 AM Gábor Malomsoki <gmalomsoki1980 using gmail.com>
> >> wrote:
> >>
> >>> Dear all,
> >>>
> >>> i have created a logistic regression model,
> >>>   on the train df:
> >>> mymodel1 <- glm(book_state ~ TG_KraftF5, data = train, family =
> >>> "binomial")
> >>>
> >>> then i try to predict with the test df
> >>> Predict<- predict(mymodel1, newdata = test, type = "response")
> >>> then iget this error message:
> >>> Error in model.frame.default(Terms, newdata, na.action = na.action, xlev =
> >>> object$xlevels)
> >>> Factor  "TG_KraftF5" has new levels
> >>>
> >>> i have tried different proposals from stackoverflow, but unfortunately
> >>> they
> >>> did not solved the problem.
> >>> Do you have any idea how to test a logistic regression model when you have
> >>> different levels in train and in test df?
> >>>
> >>> thank you in advance
> >>> Regards,
> >>> Gabor
> >>>
> >>>          [[alternative HTML version deleted]]
> >>>
> >>> ______________________________________________
> >>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> >>> 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.
> >>>
> >>
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > 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.
>
> hello,
>
> What exactly didn't work? You say you have tried the solutions found in
> stackoverflow but without a link, we don't know which answers to which
> questions you are talking about.
> Like Bert said, if you assign NA to the new levels, present only in
> test, it should work.
>
> Can you post links to what you have tried?
>
> Hope this helps,
>
> Rui Barradas