R help - Sep 2008 - ariable Importance Measure in Package RandomForest

Hi,

I've a question about the RandomForest package.

The package allows the extraction of a variable importance measure. As far as
I could see from the documentation, the computation is based on the Gini index.

Do you know if this extraction can be also based on other criteria? In
particular,
I'm interested in the info gain criterion.

Best regards,
Chris
--

Given you do not want to touch the randomForest implementation itself, 
the answer is "no, there is no particular function to do it in package 
randomForest. More particular:

?randomForest tells us that a value "importance" is returned that is
`a
matrix with nclass + 2 (for classification) or two (for regression) 
columns. For classification, the first nclass columns are the 
class-specific measures computed as mean descrease in accuracy. The 
nclass + 1st column is the mean descrease in accuracy over all classes. 
The last column is the mean decrease in Gini index. For Regression, the 
first column is the mean decrease in accuracy and the second the mean 
decrease in MSE. If importance=FALSE, the last measure is still returned 
as a vector.'

So as far as I can see, you would have to change randomForest itself 
that has to return some relevant values in order to calculate the 
criterion(s) you are interested in.

Best wishes,
Uwe Ligges






linuxkaffee at gmx.net wrote:
> Hi,
> 
> I've a question about the RandomForest package.
> 
> The package allows the extraction of a variable importance measure. As far
as
> I could see from the documentation, the computation is based on the Gini
index.
> 
> Do you know if this extraction can be also based on other criteria? In
particular,
> I'm interested in the info gain criterion.
> 
> Best regards,
> Chris
> --
> 
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