The Use of Machine Learning Algorithms in Recommender Systems: A Systematic Review.

•A survey of machine learning (ML) algorithms in recommender systems (RSs) is provided.•The surveyed studies are classified in different RS categories.•The studies are classified based on the types of ML algorithms and application domains.•The studies are also analyzed according to main and alternative performance metrics.•LNCS and EWSA are the main sources of studies in this research field.