[R] Rpart - user defined split functions

Paolo Radaelli paolo.radaelli at unimib.it
Thu May 14 18:11:20 CEST 2009

Dear all,
I'm writing my own method to be used in Rpart by defining the list of 
functions named init, split and eval. I'm following the example given in the 
file 'tests/usersplits.R' in the sources.
By now I'm able to define the split function (and it works correctly in the 
tree construction) while I have some problems with the init and the eval 
The task I'm facing with is a classification task and I'd like the eval 
function to produce an output similar to the one obtained for method="class" 
        node), split, n, loss, yval, (yprob)
I'd also like the summary.rpart function to produce an output reporting 
class counts and probabilities rows for each node and this is done modifying 
the summary function in the init one.
Unfortunately the example reported in 'tests/usersplits.R' does not consider 
this case and the other examples I found in: Therneau,  Atkinson - "An 
Introduction to Recursive Partitioning Using the RPART Routines" do not help 
me to solve the problem.
I also tried to have a look to the source code of the functions rpart.s and 
rpart.class.s but it is quite hard for me to understand which part of the 
code I should include in definining my own eval and init functions.
Does anyone can suggest me how to proceed ?
Any input would be highly appreciated.
Thank you

Paolo Radaelli
Dipartimento di Metodi Quantitativi per le Scienze Economiche ed Aziendali
Facoltà di Economia
Università degli Studi di Milano-Bicocca
Via Bicocca degli Arcimboldi, 8
20126 Milano
e-mail paolo.radaelli at unimib.it
Tel +39 02 6448 3163
Fax +39 02 6448 3105

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