R help - Sep 2008 - CLARA and determining the right number of clusters

Hi everyone

I have a question about clustering. I've managed using CLARA to get a
clustering analysis of a large data set. But now I want to find which is the
right number of clusters.

The clara.object gives some information like the ratio between maximal and
minimal dissimilarity that says (maybe if lower than 1??) if a cluster is
well-separated from the other. I've also read something about silhouette and
abut cluster.stats but can't manage to get how to find the right number of
clusters.

I've tried a suggestion from the mailing list but when using dist

d1<-dist(mydata$sst)

it says that "specified vector size is too big"

Is there any method to find the right number of clusters when using clara?
Maybe something I've tried but with a small and simple trick I can't
find

Thanks in advance

-- 
_________________________
El ponent la mou, el llevant la plou
Usuari Linux registrat: 363952
-------
Fotos: http://picasaweb.google.es/pacomet

	[[alternative HTML version deleted]]

Hi there,

generally finding the right number of clusters is a difficult problem and 
depends heavily on the cluster concept needed for the particular 
application.
No outcome of any automatic mathod should be taken for granted.

Having said that, I guess that something like the example given
in
> ?pam.object
(replacing pam by clara) should work with clara, too.

Regards,
Christian


On Tue, 30 Sep 2008, pacomet wrote:
> Hi everyone
>
> I have a question about clustering. I've managed using CLARA to get a
> clustering analysis of a large data set. But now I want to find which is
the
> right number of clusters.
>
> The clara.object gives some information like the ratio between maximal and
> minimal dissimilarity that says (maybe if lower than 1??) if a cluster is
> well-separated from the other. I've also read something about
silhouette and
> abut cluster.stats but can't manage to get how to find the right number
of
> clusters.
>
> I've tried a suggestion from the mailing list but when using dist
>
> d1<-dist(mydata$sst)
>
> it says that "specified vector size is too big"
>
> Is there any method to find the right number of clusters when using clara?
> Maybe something I've tried but with a small and simple trick I
can't find
>
> Thanks in advance
>
> -- 
> _________________________
> El ponent la mou, el llevant la plou
> Usuari Linux registrat: 363952
> -------
> Fotos: http://picasaweb.google.es/pacomet
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at 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.
>
*** --- ***
Christian Hennig
University College London, Department of Statistical Science
Gower St., London WC1E 6BT, phone +44 207 679 1698
chrish at stats.ucl.ac.uk, www.homepages.ucl.ac.uk/~ucakche