sil: Silhouette index and plot

Description

This function creates silhouette indices and silhouette plots of each cluster. The plot presents also the mean of the silhouette indices per cluster.

Usage

sil(distdata, idmedoid, idcluster, title = "")

Value

Function returns a list with following components:

result is a data frame of the silhouette indices for all objects

plot is the silhouette plots of each cluster.

Arguments

distdata: A distance matrix (n x n) or dist object.
idmedoid: A vector of id medoids (see Details).
idcluster: A vector of cluster membership (see Details).
title: A title of the plot.

Author

Weksi Budiaji
Contact: budiaji@untirta.ac.id

Details

The silhouette index of object i is calculated by $$si(i)=\frac{b_i-a_i}{max(a_i, b_i)}$$ where $a_i$ is the average distance of object i to all objects within the cluster, and $b_i$ is the average distance of object i to all objects within the nearest cluster.

The idmedoid argument corresponds to the idcluster argument. If the length of idmedoid is 3, for example, the idcluster has to have 3 unique memberships, or it returns Error otherwise. The length of the idcluster has also to be equal to n (the number of objects).

References

P. J. Rousseeuw. 1987 Silhouettes: a graphical aid to the interpretation and validation of cluster analysis. Journal of Computational and Applied Mathematics, vol. 20, pp. 53-65

Examples

Run this code

distiris <- as.matrix(dist(iris[,1:4]))
res <- fastkmed(distiris, 3)
silhouette <- sil(distiris, res$medoid, res$cluster)
silhouette$result[c(1:3,70:75,101:103),]
silhouette$plot

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