Two-stage clustering in R

Question

• Is it possible to do 2-stage cluster analysis in R?
• Can anybody provide me resource on it?

Answer 1

The closest package that I can think of is birch, but it is not available on CRAN anymore so you have to get the source and install it yourself (R CMD install birch_1.1-3.tar.gz works fine for me, OS X 10.6 with R version 2.13.0 (2011-04-13)). It implements the original algorithm described in

Zhang, T. and Ramakrishnan, R. and Livny, M. (1997). BIRCH: A New Data Clustering Algorithm and Its Applications. Data Mining and Knowledge Discovery, 1, 141-182.

which relies on cluster feature tree, as does SPSS TwoStep (I cannot check, though). There's a possibility of using the k-means algorithm to perform clustering on birch object (kmeans.birch()), that is partition the subclusters into k groups such that the sum of squares of all the points in each subcluster to the assigned cluster centers is minimized.