[R] rpart

Ko-Kang Kevin Wang k.wang at auckland.ac.nz
Fri Jun 4 10:07:45 CEST 2004


I think most, if not all, your questions can be answered by:

1) ?rpart

2) Some search through the r-help mailing list

3) Read the chapter on tree-based models in MASS 4 (Modern Applied
Statistics with S) by Venables and Ripley


----- Original Message ----- 
From: <h0444k87 at student.hu-berlin.de>
To: <r-help at stat.math.ethz.ch>
Sent: Friday, June 04, 2004 9:59 PM
Subject: [R] rpart

> Hello everyone,
> I'm a newbie to R and to CART so I hope my questions don't seem too
> 1.)
> My first question concerns the rpart() method. Which method does rpart use
> order to get the best split - entropy impurity, Bayes error (min. error)
or Gini
> index? Is there a way to make it use the entropy impurity?
> The second and third question concern the output of the printcp()
> 2.)
> What exactly are the cps in that sense here? I assumed them to be the
> complexity parameters as in Breiman et al., 1998, Section 3.3? Are they
the same
> as the treshold niveaus of alpha? I have read somewhere that the cps here
> the  treshold alphas divided by the root node error. Is that true?
> 3.)
> How is rel error computed?
> I am supposed to evaluate the goodness of classification of of the CART
> Do you think rel error is a good measure for that?
> I'd be very thankful if anyone could give me hand on that. This is a
project for
> uni and I desperately need a good mark.
> Thank you very much in advance,
> Mareike
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