[R] Question about rpart(sth~.,database)
Grześ
gregorio99 at gmail.com
Mon Apr 20 00:19:29 CEST 2009
Gavin Simpson wrote:
>
> Grześ wrote:
>> I have a standard database - HouseVotes84
>> For example:
>> Class V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 V13 V14 V15 V16
>> 1 republican n y n y y y n n n y <NA> y y y n y
>> 2 republican n y n y y y n n n n n y y y n <NA>
>> 3 democrat <NA> y y <NA> y y n n n n y n y y n n
>> .
>> .
>> .
>> end I build a tree like this:
>>> hv.tree1=rpart(Class~.,HouseVotes84)
>> everything is ok! My question is:
>> What exactly mean "Class~.,"?
>
> It means include all remaining variables in HouseVotes84 on the rhs of
> the formula, i.e. as variables that should be used to predict the Class
> variable.
>
>>
>> Why when I use "Class~.," - then I get the best solution but when I use
>> as a
>> parameter like this:
>>> hv.tree2=rpart(V2~.,HouseVotes84)
>
> Why does this surprise you? You are now trying to predict the variable
> V2 (y/n) from Class and all remaining variables.
>
>> I also get solution but not such good like before.
>
> They are solutions to two different problems.
>
> If you want to predict Class, then you need
>
> Class ~ ., data = HouseVotes84
>
> or, to specify exactly which variables to use as predictors of Class,
> state them explicitly:
>
> Class ~ V1 + V3 + V4, data = HouseVotes84
>
> I think you should look at the documentation that comes with R (An
> Introduction to R) or some of the contributed help documents on the R
> Website to read up on model formulae and how to represent models using
> this notation.
>
> HTH
>
> G
>
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.
>
>
Thank you very much!
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