My question is about the preProcess() argument in Caret package. This argument can use median, knn, or bagImpute.
If a dataset has mixed data (categorical and numerical predictors), and both kinds of predictors have NAs, what does caret do behind the scenes with the categorical/factor variables?
After reading the Caret documentation I think currently Caret ignore the factor variables (at least for standarization). If this is correct, is there no imputation for categorical predictors?
I think mice package does imputation for categorical variables: multinomial logistic regression.
In general terms, is it wise to impute on categorical predictors?, what is the way to follow in the case of caret?