Regularized K-means through hard-thresholding

We study a framework for performing regularized K-means, based on direct penalization of the size of the cluster centers. Different penalization strategies are considered and compared in a theoretical analysis and an extensive Monte Carlo simulation study. Based on the results, we propose a new method called hard-threshold K-means (HTK-means), which uses an ℓ0 penalty to induce sparsity. HTK-means is a fast and competitive sparse clustering method which is easily interpretable, as is illustrated on several real data examples. In this context, new graphical displays are presented and used to gain further insight into the data sets.