[R] rpart - the xval argument in rpart.control and in xpred.rpart

[Terry Therneau]

> I have some problems in understanding the meaning of the xval argument in 
> the two functions rpart.control and xpred.rpart. In the former it is defined 
> as the number of cross-validations while in the latter it is defined as the 
> number of cross-validation groups. 

  It is the same thing.  If xval=10 then the data is divided into 10 disjoint 
groups.  A model is fit with group 1 left out and that model is used to predict 
the observations in group 1; then a model is fit with group 2 left out; then 
group 3, ...
   So 10 groups = 10 fits of the model.
   
   
   
   	Terry Therneau