What is unsupervised learning?
unsupervised learning, we where observe only the features X1, X2, . . . , Xp. We are not interested in prediction, because we do not have an associated response variable Y .
goal of unsupervised learning
The goal is to discover interesting things about the measurements: is there an informative way to visualize the data? Can we discover subgroups among the variables or among the observations?
What are two methods of unsupervised learning?

The Challenge of Unsupervised Learning

Advantage of unsupervised learning

Principal Components Analysis

Principal Components Analysis: details

PCA: example
