Ways of clustering

This post is more of informative than tutorial... it will introduce the different methods applied in clustering.

The clustering methods are usually divided into two broad categories: Flat clustering and Hierarchical clustering. Flat clustering is fast but requires a earlier knowledge of approximate number of clusters to be make and also it is unstructured. Hierarchical clustering is slower, at least quadratic in time but has a structure of hierarchy which is very helpful as mentioned earlier, also it doesn't require the knowledge of number of clustered to be made.

Flat clustering is usually done by K-means and Expectation-Maximization Algorithm maximization algorithm or EM algorithm.

Hierarchical clustering is usually done by HAC or hierarchy agglomerative clustering:a bottom-up clustering algorithm ,usually done with different measures :single-link,complete-link,group-average,centroid,etc. Other approach for Hierarchical clustering can be top-down or divisive clustering clustering.