Incremental learning of variable rate concept drift

We have recently introduced an incremental learning algorithm, Learn ⁺⁺.NSE, for Non-Stationary Environments, where the data distribution changes over time due to concept drift. Learn^{+ +}.NSE is an ensemble of classifiers approach, training a new classifier on each consecutive batch of data that become available, and combining them through an age-adjusted dynamic error based weighted majority voting. Prior work has shown the algorithm's ability to track gradually changing environments as well as its ability to retain former knowledge in cases of cyclical or recurring data by retaining and appropriately weighting all classifiers generated thus far. In this contribution, we extend the analysis of the algorithm to more challenging environments experiencing varying drift rates; but more importantly we present preliminary results on the ability of the algorithm to accommodate addition or subtraction of classes over time. Furthermore, we also present comparative results of a variation of the algorithm that employs an error-based pruning in cyclical environments.