Multistream classification with relative density ratio estimation

Abstract

In supervised learning, availability of sufficient labeled data is of prime importance. Unfortunately, they are sparingly available in many real-world applications. Particularly when performing classification over a non-stationary data stream, unavailability of sufficient labeled data undermines the classifier's long-term performance by limiting its adaptability to changes in data distribution over time. Recently, studies in such settings have appealed to transfer learning techniques over a data stream while detecting drifts in data distribution over time. Here, the data stream is represented by two independent non-stationary streams, one containing labeled data instances (called source stream) having a biased distribution compared to the unlabeled data instances (called target stream). The task of label prediction under this representation is called Multistream Classification, where instances in the two streams occur independently. While these studies have addressed various challenges in the multistream setting, it still suffers from large computational overhead mainly due to frequent bias correction and drift adaptation methods employed. In this paper, we focus on utilizing an alternative bias correction technique, called relative density-ratio estimation, which is known to be computationally faster. Importantly, we propose a novel mechanism to automatically learn an appropriate mixture of relative density that adapts to changes in the multistream setting over time. We theoretically study its properties and empirically demonstrate its superior performance, within a multistream framework called MSCRDR, on benchmark datasets by comparing with other competing methods.