R help - Jun 2004 - rpart

Hi,

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

Kevin

----- 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
stupid.
>
> 1.)
> My first question concerns the rpart() method. Which method does rpart use
in
> 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()
function.
> 2.)
> What exactly are the cps in that sense here? I assumed them to be the
treshold
> 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
are
> 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
method.
> 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
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>

Hello everyone,

I'm a newbie to R and to CART so I hope my questions don't seem too
stupid.

1.)
My first question concerns the rpart() method. Which method does rpart use in
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() function.
2.)
What exactly are the cps in that sense here? I assumed them to be the treshold
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 are
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 method.
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