[R] (Cross-)validating GLM including factors

[Roland Pape]

Dear list,

I would like to validate various GLMs, all of them containing (among others) several factors as predictors. I thought about using cv.glm from the boot package, but necessarily got the error "factor xy has new level z". Is there any function to easily cross validate LMs or GLMs containing factors that I have missed, or any other work around?
- Having in mind that using cross validation on a small data set is not the best solution (I have 50-600 samples, but also three factors with up to 15 levels): Are there any other approaches?

Any help is greatly appreciated!

Roland

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