Have you checked Apache Mahout recommendation framework ( https://mahout.apache.org/docs/latest/algorithms/recommenders/ https://mahout.apache.org/docs/latest/a

Have you checked Apache Mahout recommendation framework ( https://mahout.apache.org/docs/latest/algorithms/recommenders/ https://mahout.apache.org/docs/latest/algorithms/recommender... )? For 'small data' it can be used as Java library (algorithms for single-machine); if you prefer .NET C# port is also present: https://github.com/nreco/recommender https://github.com/nreco/recommender . If you're new to collaborative filtering 'Apache Mahout in Action' book will help a much.