RE: [R] Gini's Importance Value Variable = Inf

From: Liaw, Andy <andy_liaw_at_merck.com>
Date: Thu 24 Mar 2005 - 08:14:03 EST


That result looks fishy: Not only there shouldn't be Inf, but there shouldn't be negative values in that measure (look at V6). I will look into it.

I hope by now you realize that there's not much point in asking such package-specific questions on R-help... Not all package maintainers are on R-help, and they are the best persons to ask package specific questions or report bugs.

Andy

> From: Melanie Vida
>
> Hi All,
>
> In the script below, the importance measure for column 4 (ie
> MeanDecreaseGini) indicated "Inf" for V7.
> Running the getTree command showed that "V7" had been
> selected at least
> twice in one of the trees for Random Forest. So the "Inf" command was
> not generated as a result of dividing the sum of the decreases by 0.
>
> Any suggestions on what may be causing the Inf in "V7" would
> be helpful?
> Thanks in advance,
>
> -Melanie
>
> ---------i
>
> library(randomForest)
>
> credit<-read.csv(url("ftp://ftp.ics.uci.edu/pub/machine-learni
> ng-databases/credit-screening/crx.data"),
> header=FALSE, na.string="?")
>
> credit.rf <- randomForest(V16~., credit, imp=T,
> do.trace=100,na.action=na.omit)
>
> imp <- round(importance(credit.rf), 2)
>
> imp
> - + MeanDecreaseAccuracy MeanDecreaseGini
> V1 0.00 0.00 0.00 0.00
> V2 0.75 0.25 0.55 19.92
> V3 0.41 0.57 0.46 22.13
> V4 0.39 0.33 0.33 4.93
> V5 0.26 0.24 0.21 0.60
> V6 0.39 0.50 0.40 -46.21
> V7 0.91 0.59 0.71 Inf
> V8 1.35 1.35 1.06 37.15
> V9 0.00 0.00 0.00 0.00
> V10 0.00 0.00 0.00 0.00
> V11 1.65 1.59 1.23 49.16
> V12 0.00 0.00 0.00 0.00
> V13 -0.11 -0.10 -0.10 0.21
> V14 0.82 0.57 0.66 20.71
> V15 1.36 1.02 1.01 33.47
>
> getTree(credit.rf, 1)
>
> left daughter right daughter split var split point status prediction
> [1,] 2 3 15 492.0000
> 1 0
> [2,] 4 5 11 2.5000
> 1 0
> [3,] 6 7 2 38.5000
> 1 0
> [4,] 8 9 14 83.0000
> 1 0
> [5,] 10 11 7 207.0000
> 1 0
> [6,] 12 13 11 0.5000
> 1 0
> [7,] 0 0 0 0.0000
> -1 2
> [8,] 14 15 7 117.0000
> 1 0
> [9,] 16 17 8 3.0625
> 1 0
> [10,] 18 19 3 0.2700
> 1 0
> [11,] 0 0 0 0.0000
> -1 2
> [12,] 20 21 15 4753.0000
> 1 0
> [13,] 22 23 2 37.0850
> 1 0
> [14,] 24 25 14 8.5000
> 1 0
>
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R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu Mar 24 08:20:31 2005

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