Definition
User-based Nearest-neighbour Collaborative Filtering (Recommendation)
User-based nearest-neighbour collaborative filtering is a collaborative filtering method that predicts an active user
‘s rating of an unseen item from the ratings given by users whose past ratings resemble those of . Let
be the users most similar to among those who have rated . The basic unweighted estimate is The method finds peers using items rated by both users, transfers those peers’ ratings of
to , and repeats this estimate for every item unseen by . The items with the largest predicted ratings are recommended. Variants weight each peer by user similarity or correct for differences in users’ typical rating levels.