[R] CV by rpart/mvpart

[Terry Therneau]

  The rpart function allows one to give the cross-validation groups explicitly.
So if the number of observations was 10, you could use
   > rpart( y ~ x1 + x2, data=mydata, xval=c(1,1,2,2,3,3,1,3,2,1))
which causes observations 1,2,7, and 10 to be left out of the first xval
sample, 3,4, and 9 out of the second, etc.   

 I was going to write "read the manual page for control.rpart", but it seems
I forgot to put this feature into the documentation!  

	Terry Therneau
	
> On 12/28/06, Pedro Ramirez <palmar379 at yahoo.es> wrote:
>> Dear R-list,
>>
>> I am using the rpart/mvpart-package for selecting a right-sized 
>> regression tree by 10-fold cross-validation. My question: Is there a 
>> possibility to find out for every observation in which of the ten folds 
>> it is lying? I want to use the same folds for validating another 
>> regression method (moving averages) in order to choose the better one.
>>
>> Thanks a lot,
>> Pedro