16.2 Cluster Analysis
Cluster analysis or clustering is the task of grouping a set of objects in such a way that objects in the same group (a cluster) are more similar (in some sense or another) to each other than to those in other groups (clusters).
We seek to partition observations into distinct groups so that the observations within each group are quite similar to each other, while observations in different groups are quite different from each other.
To make this concrete, we must define what it means for two or more observations to be similar or different
- most often this is done by the measurement of distance
- cluster analysis methods work from dissimilarity measures (e.g., distance matrix)