Hi Andy,

Thank you for your response.

I've already came by this function but also noticed that the help file
states that:
"This method does *not* currently provide class–specific measures of
importance when the *response is a factor*."

Which is the case I need to deal with.

Any suggestions as to how to adjust this function for the factor-response
case?


Best,
Tal




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On Mon, Jan 24, 2011 at 5:21 PM, Liaw, Andy <andy_liaw@merck.com> wrote:

> Check out caret::varImp.rpart().  It's described in the original CART
> book.
>
> Andy
>
> From: Tal Galili
> >
> > Hello all,
> >
> > When building a CART model (specifically classification tree)
> > using rpart,
> > it is sometimes interesting to know what is the importance of
> > the various
> > variables introduced to the model.
> >
> > Thus, my question is: *What common measures exists for
> > ranking/measuring
> > variable importance of participating variables in a CART
> > model? And how can
> > this be computed using R (for example, when using the rpart package)*
> >
> > For example, here is some dummy code, created so you might show your
> > solutions on it. This example is structured so that it is clear that
> > variable x1 and x2 are "important" while (in some sense) x1 is more
> > important then x2 (since x1 should apply to more cases, thus make more
> > influence on the structure of the data, then x2).
> >
> > set.seed(31431)
> >
> > n <- 400
> >
> > x1 <- rnorm(n)
> >
> > x2 <- rnorm(n)
> >
> > x3 <- rnorm(n)
> >
> > x4 <- rnorm(n)
> >
> > x5 <- rnorm(n)
> >
> > X <- data.frame(x1,x2,x3,x4,x5)
> >
> > y <- sample(letters[1:4], n, T)
> >
> > y <- ifelse(X[,2] < -1 , "b", y)
> >
> > y <- ifelse(X[,1] < 0 , "a", y)
> >
> > require(rpart)
> >
> > fit <- rpart(y~., X)
> >
> > plot(fit); text(fit)
> >
> > info.gain.rpart(fit) # your function - telling us on each variable how
> > important it is
> >
> > (references are always welcomed)
> >
> >
> > Thanks!
> >
> > Tal
> >
> > ----------------Contact
> > Details:-------------------------------------------------------
> > Contact me: Tal.Galili@gmail.com |  972-52-7275845
> > Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il
> > (Hebrew) |
> > www.r-statistics.com (English)
> > --------------------------------------------------------------
> > --------------------------------
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
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