[R] randomForest and ordered factors

[Birgit Lemcke]

Hello Andy,

thanks for your answer and sorry that I did not check the rfNews.
You are right, presently I am only looking at variable importance and  
therefore I am very happy to hear that I won`t have problems using  
ordered factors.
Since I just started to fiddle around with randomForest it might be  
that I will have some more questions later - let`see.

But presently I am very grateful that you provide this package.

Greets

Birgit

Am 29.04.2008 um 16:29 schrieb Liaw, Andy:
> If you are using the latest version (4.5-25), you will see in rfNews 
> () that that's the problem I need to fix.  The package was able to  
> handle ordered factors, but some more stringent checks for factor  
> levels consistency introduced in 4.5-23 broke the support for  
> ordered factors in prediction.
>
>> From the code you've shown, it looks like you are just growing the  
>> forest to evaluate variable importance or other things, instead of  
>> predicting other data (since you set keep.forest=FALSE).  If  
>> that's the case, you should be fine, as the problem only happens  
>> when you try to call predict() with models that contain ordered  
>> factors as predictors.
>
> (Ordered factors are basically treated as numerics in RF: trees  
> only make use of ranks for numeric variables, so there's basically  
> no difference between ordered factors and numeric variables as  
> predictors.)
>
> Andy
>
> From: Birgit Lemcke
>>
>> Hello R-user!
>>
>> I am running R 2.7.0 on a Power Book (Tiger). (I am still R and
>> statistics beginner)
>>
>> I try to find the most important variables to divide my dataset as
>> given in a categorical variable.
>>
>> code:
>>
>> Test.rf4<-randomForest(Sex~.,na.action=na.roughfix, data=Subset4,
>> importance=TRUE, proximity=TRUE, ntree=10000, do.trace=1000,
>> keep.forest=FALSE)
>>
>> My dataset contains also ordered factors classified as such.
>> Is randomForest able to deal with it, does it change anything or is
>> there no difference in using factors or ordered factors?
>>
>> Many thanks in advance
>>
>> B.
>>
>> Birgit Lemcke
>> Institut für Systematische Botanik
>> Zollikerstrasse 107
>> CH-8008 Zürich
>> Switzerland
>> Ph: +41 (0)44 634 8351
>> birgit.lemcke at systbot.uzh.ch
>>
>> 175 Jahre UZH
>> «staunen.erleben.begreifen. Naturwissenschaft zum Anfassen.»
>> MNF-Jubiläumsevent für gross und klein.
>> 19. April 2008, 10.00 Uhr bis 02.00 Uhr
>> Campus Irchel, Winterthurerstrasse 190, 8057 Zürich
>> Weitere Informationen http://www.175jahre.uzh.ch/naturwissenschaft
>>
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>>
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Birgit Lemcke
Institut für Systematische Botanik
Zollikerstrasse 107
CH-8008 Zürich
Switzerland
Ph: +41 (0)44 634 8351
birgit.lemcke at systbot.uzh.ch

175 Jahre UZH
«staunen.erleben.begreifen. Naturwissenschaft zum Anfassen.»
MNF-Jubiläumsevent für gross und klein.
19. April 2008, 10.00 Uhr bis 02.00 Uhr
Campus Irchel, Winterthurerstrasse 190, 8057 Zürich
Weitere Informationen http://www.175jahre.uzh.ch/naturwissenschaft