[R] Clustering and Calinski's index

[David Wartel]

I have to solve a clustering problem.
My first step is to determinate the number of clusters, that's why I 'm using 
the Calinski index ( [tr(b)/(k-1)]/[tr(w)/(k-1)] )  which i try to maximize  
to have the best number of clusters.
A function is already implemented in R to calculate this index :

clustIndex(cl,x, index="calinski")

where cl is the result of a clustering method , for instance:

cclust(x,k,itermax,verbose=TRUE,method="kmeans")

My probleme is that I can't calculate the Calinski's index when a cluster 
contains only one datapoint :

Error in cov(x[cluster == l, ]) : supply both x and y or a matrix-like x


Is there a way to solve this?

thanx for your help,

David

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