Combinatorial PCA and SVM methods for feature selection in learning classifications (applications to text categorization)

In this paper we describe a purely combinatorial approach of obtaining meaningful representations of text data. More precisely, we describe two different methods that materialize this approach: we call them combinatorial principal component analysis (cPCA) and combinatorial support vector machines (cSVM). These names emphasise mathematical analogies between the well known PCA and SVM, on one hand, and our respective methods. For evaluating the selected spaces of features, we used the environment set for TREC 2002 and used a very common classifier: 1-nearest neighbour (1-NN). We compared the results obtained on the feature sets calculated by the procedures we described (cPCA and cSVM) with the results obtained on the original feature space. We showed that by selecting a feature space on average 50 times smaller than the original space, the performance of the classifier does not decrease by more than 2%.