Recommender Systems: When Memory Matters

In this paper, we study the effect of non-stationarities and memory in the learnability of a sequential recommender system that exploits user's implicit feedback. We propose an algorithm, where model parameters are updated user per user by minimizing a ranking loss over blocks of items constituted by a sequence of unclicked items followed by a clicked one. We illustrate through empirical evaluations on four large-scale benchmarks that removing non-stationarities, through an empirical estimation of the memory properties, in user's behaviour interactions allows to gain in performance with respect to MAP and NDCG.