Sequential dimension reduction and clustering of mixed-type data

Clustering of a set of objects described by a mixture of continuous and categorical variables can be a challenging task. In the context of data reduction, an effective class of methods combine dimension reduction with clustering in the reduced space. In this paper, we review three approaches for sequential dimension reduction and clustering of mixed-type data. The first step of each approach involves the application of principal component analysis on a suitably transformed matrix. In the second step, a partitioning or hierarchical clustering algorithm is applied to the object scores in the reduced space. The common theoretical underpinnings of the three approaches are highlighted. The results of a benchmarking study show that sequential dimension reduction and clustering is an effective strategy, especially when categorical variables are more informative than continuous with regard to the underlying cluster structure. Strengths and limitations are also demonstrated on a real mixed-type dataset.