[R] Re: your mail about rpart

[Prof Brian Ripley]

Add NAOK=T to the .C call in formatg.  It won't help you much, though.


On Wed, 2 Jan 2002, Davies, Bob wrote:

> Any rpart user:
>
> I am trying to construct an rpart tree using a subset of the data and it
> will occasionally fail when predicting a categorical response variable.
>
> The reason that rpart fails is that the subset does not contain each of the
> categories present in the original data.  For example, in the car.test.frame
> example, a subset that has all the categories except "Small" will not
> produce an rpart tree.
>
> I attempted to use "parms=list(prior=...) and it did not correct the
> problem.
>
> Here is a demonstration of the problem using the car.test.frame:
>
> library(rpart)
> data(car.test.frame)
> t1 <- rpart(Type ~ ., car.test.frame)
> t1
> sub <- row.names(car.test.frame[car.test.frame[,"Weight"] > 2567.5,])  #
> create a subset
> rpart (Type ~ ., car.test.frame, subset=sub )  # this statement will fail
>
> # so now attempt to indicate what the priors should look like:
> rpart (Type ~ ., car.test.frame, subset=sub,
> parms=list(prior=t1$parms$prior))  # this statement will fail
>
> # now add 1 "Small" car to this subset of car.test.frame
> sub <- row.names(car.test.frame[car.test.frame[,"Weight"] > 2559,])  # lower
> the weight just a little to get a "Small" car.
> rpart(Type ~ ., car.test.frame, subset=sub) # This statement will work !
>
> Any suggestions?
>
> I am using R 1.4.0 on Windows 2000.
>
> Bob Davies
>
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-- 
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

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