On Thu, 2 Aug 2001, Shuguang Chen wrote:
> Our understanding of how classification trees in Rpart treat missing is
> that if the variable is ordinal(continous), Rpart, by default, imputes a
> value for missing. How do we do the classification tree and tell Rpart not
> to impute. That is, what command is used to turn off the imputation.
Not true. Please do read the technical report (included in rpart_2.x).
Like CART (the book and the program), rpart uses surrogate splits.
To turn that off (why?) see ?rpart.control.
> Also, if we do get true missing, how does classification tree analysis in
> Rpart treat missing when the variable is ordinal (after we tell Rpart not
> to impute)? I believe that when a variable is categorical, missing is
> treated as just another category. But if the variable is ordinal, for
Not true.
> example, if the question is, how satsified are you with such and such, and
> the response goes on a 1-5 scale, is the missing treated as another
'value'
> on the scale, as a categorical response independent of the 1-5 scale, or as
> not part of the response at all, e.g., missing?
You seem to be confusing rpart with something else (it looks like with
trees in S).
--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272860 (secr)
Oxford OX1 3TG, UK Fax: +44 1865 272595
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !) To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._