Re: [R] cluster

From: Christian Hennig <chrish_at_stats.ucl.ac.uk>
Date: Wed 27 Jul 2005 - 04:39:04 EST

Dear Weiwei,

your question sounds a bit too general and complicated for the R-list. Perhaps you should look for personal statistical advice. The quality of methods (and especially distance choice) for down-sampling ceratinly depends on the structure of the data set. I do not see at the moment why you need any down-sampling at all, and you should find out first if and why it's a good thing to do (by whatever method).

An obvious candidate for a clustering algorithm would be pam/clara in package cluster, because this approach chooses points already in the data set as cluster centroids (and produces therefore a proper subsample), which does not apply to most other clustering methods.

However, in
 C. Hennig and L. J. Latecki: The choice of vantage objects for image retrieval. Pattern Recognition 36 (2003), 2187-2196. the clustering approach has been clearly outperformed by some stepwise selection approaches for down-sampling - admittedly in a different kind of problem, but I think that the reasons for this may apply also to your situation,

You can compare different clusterings (or choices of a subset) by cross-validation or
bootstrap applied to the resulting decision tree in the classification problem.

Best,
Christian

On Mon, 25 Jul 2005, Weiwei Shi wrote:

> Dear listers:
>
> Here I have a question on clustering methods available in R. I am
> trying to down-sampling the majority class in a classification problem
> on an imbalanced dataset. Since I don't want to lose information in
> the original dataset, I don't want to use naive down-sampling: I think
> using clustering on the majority class' side to select
> "representative" samples might help. So, my question is, which
> clustering method should be tested to get the best result. I think the
> key thing might be the selection of "distance" considering the next
> step in which I would like to use decision trees.
>
> Please share your experience in using clustering (Any available
> implementation outside R is also welcome)
>
> weiwei
> --
> Weiwei Shi, Ph.D
>
> "Did you always know?"
> "No, I did not. But I believed..."
> ---Matrix III
>
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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 Wed Jul 27 04:43:41 2005

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