In general, you can toss any set of numbers into a clustering algorithm, and it's kind of interesting to puzzle over the structures that come out. The more you

In general, you can toss any set of numbers into a clustering algorithm, and it's kind of interesting to puzzle over the structures that come out. The more you know about the domain, the more interesting it tends to be. PCA can be the same way. You toss images or whatever in, and out come either eigenvectors or principal components of the images. Either way it's often interesting to domain experts.