Feature Transformation and Dimensionality Reduction

Abstract

In the previous chapters, we focused on feature subset selection. We now discuss related and/or less developed topics with respect to feature transformation and dimensionality reduction. The first two sections are about feature trans- formation, which introduce techniques in Statistics, Machine Learning, and Knowledge Discovery. The third section discusses feature discretization which is closely related to dimensionality reduction. If subset selection allows reduction in one dimension, feature discretization could enable reduction along two dimensions. In the fourth section, we go beyond the classification model and explore feature selection without class information. Data without class information are unsupervised data (unlabeled). As we move from supervised (labeled) data to unsupervised data, we also step into a territory that is not as well explored as feature selection for classification. However, we foresee the rising need for unsupervised feature selection and expect more work to be carried out in the near future.