# Cluster Analysis

Cluster analysis is a form of *unsupervised* learning which aims to discover and explore the underlying structure in the data. The crux of a cluster analysis algorithm is distance metrics: the way you measure similarity or distance between observations. Unsupervised learning is often used in situations where you do not have labelled data (perhaps it is expensive) or when you might not know the correct values for some of your data and therefore, you might want to evaluate its underlying structure.