Which app will you use next? Collaborative filtering with interactional context

The application a smart phone user will launch next intu- itively depends on the sequence of apps used recently. More generally, when users interact with systems such as shop- ping websites or online radio, they click on items that are of interest in the current context. We call the sequence of clicks made in the current session interactional context. It is desirable for a recommender system to use the context set by the user to update recommendations. Most current context-aware recommender systems focus on a relatively less dynamic representational context defined by attributes such as season, location and tastes. In this paper, we study the problem of collaborative fltering with interactional con- text, where the goal is to make personalized and dynamic recommendations to a user engaged in a session. To this end, we propose the iConRank algorithm that works in two stages. First, users are clustered by their transition behav- ior (one-stepMarkov transition probabilities between items), and cluster-level Markov models are computed. Then per- sonalized PageRank is computed for a given user on the corresponding cluster Markov graph, with a personalization vector derived from the current context. We give an in- terpretation of the second stage of the algorithm as adding an appropriate context bias, in addition to click bias (or rating bias), to a classical neighborhood-based collabora- tive fltering model, where the neighborhood is determined from a Markov graph. Experimental results on two real- life datasets demonstrate the superior performance of our algorithm, where we achieve at least 20% (up to 37%) im- provement over competitive methods in the recall level at top-20.