Generation of coalition structures to provide proper groups' formation in group recommender systems

Group recommender systems usually provide recommendations to a fixed and predetermined set of members. In some situations, however, there is a set of people (N) that should be organized into smaller and cohesive groups, so it is possible to provide more effective recommendations to each of them. This is not a trivial task. In this paper we propose an innovative approach for grouping people within the recommendation problem context. The problem is modeled as a coalitional game from Game Theory. The goal is to group people into exhaustive and disjoint coalitions so as to maximize the social welfare function of the group. The optimal coalition structure is that with highest summation over all social welfare values. Similarities between recommendation system users are used to define the social welfare function. We compare our approach with K-Means clustering for a dataset from Movielens. Results have shown that the proposed approach performs better than K-Means for both average group satisfaction and Davies-Bouldin index metrics when the number of coalitions found is not greater than 4 (K <= 4) for a population size of 12 (N = 12).