Feature learning in feature-sample networks using multi-objective optimization

Data and knowledge representation are fundamental concepts in machine learning. The quality of the representation impacts the performance of a learning model directly. Feature learning transforms or enhances raw data to structures that are effectively exploited by those methods. In recent years, several works have been using complex networks for data representation and analysis. However, no feature learning method has been proposed to enhance such category of representation. Here, we present an unsupervised feature learning mechanism that works on datasets with binary features. First, the dataset is mapped into a feature-sample network. Then, a multi-objective optimization process selects a set of new vertices to produce an enhanced version of the network. The new features depend on a nonlinear function of a combination of preexisting features. Effectively, the process projects the input data into a higher-dimensional space. To solve the optimization problem, we design two metaheuristics based on the lexicographic genetic algorithm and the improved strength Pareto evolutionary algorithm (SPEA2). We show that the enhanced network contains more useful information and can be exploited to improve the performance of machine learning methods. The advantages and disadvantages of each optimization strategy are discussed.