Fast Shapelets: A Scalable Algorithm for Discovering Time Series Shapelets

Abstract

Time series shapelets are a recent promising concept in time series data mining. Shapelets are time series snippets that can be used to classify unlabeled time series. Shapelets not only provide interpretable results, which are useful for domain experts and developers alike, but shapelet-based classifiers have been shown by several independent research groups to have superior accuracy on many datasets. Moreover, shapelets can be seen as generalizing the lazy nearest neighbor classifier to an eager classifier. Thus, as a deployed classification tool, shapelets can be many orders of magnitude faster than any rival with comparable accuracy. Although shapelets are a useful concept, the current literature bemoans the fact that shapelet discovery is a time-consuming task. In spite of several efforts to speed up shapelet discovery algorithms, including the use of specialist hardware, the current state-of-the-art algorithms are still intractable on large datasets. In this work, we propose a fast shapelet discovery algorithm that outperforms the current state-of-the-art by two or three orders of magnitude, while producing models with accuracy that is not perceptibly different.