R in Action, Third Edition

16 Cluster analysis

This chapter covers

• Identifying cohesive subgroups (clusters) of observations
• Determining the number of clusters present
• Obtaining a nested hierarchy of clusters
• Obtaining discrete clusters

Cluster analysis is a data-reduction technique designed to uncover subgroups of observations within a dataset. It allows you to reduce a large number of observations to a much smaller number of clusters or types. A cluster is defined as a group of observations that are more similar to each other than they are to the observations in other groups. This isn’t a precise definition, and that fact has given rise to an enormous variety of clustering methods.

Cluster analysis is widely used in the biological and behavioral sciences, marketing, ...