Domokos Miklós Kelen created FLINK-4712:
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Summary: Implementing ranking predictions for ALS
Key: FLINK-4712
URL: https://issues.apache.org/jira/browse/FLINK-4712
Project: Flink
Issue Type: New Feature
Components: Machine Learning Library
Reporter: Domokos Miklós Kelen
We started working on implementing ranking predictions for recommender systems.
Ranking prediction means that beside predicting scores for user-item pairs, the
recommender system is able to recommend a top K list for the users.
Details:
In practice, this would mean finding the K items for a particular user with the
highest predicted rating. It should be possible also to specify whether to
exclude the already seen items from a particular user's toplist. (See for
example the 'exclude_known' setting of [Graphlab Create's ranking factorization
recommender|https://turi.com/products/create/docs/generated/graphlab.recommender.ranking_factorization_recommender.RankingFactorizationRecommender.recommend.html#graphlab.recommender.ranking_factorization_recommender.RankingFactorizationRecommender.recommend].
The output of the topK recommendation function could be in the form of
DataSet[(Int,Int,Int)], meaning (user, item, rank), similar to Graphlab
Create's output. However, this is arguable: follow up work includes
implementing ranking recommendation evaluation metrics (such as precision@k,
recall@k, ndcg@k), similar to [Spark's
implementations|https://spark.apache.org/docs/1.5.0/mllib-evaluation-metrics.html#ranking-systems].
It would be beneficial if we were able to design the API such that it could be
included in the proposed evaluation framework (see
[5157|https://issues.apache.org/jira/browse/FLINK-2157]), which makes it
neccessary to consider the possible output type DataSet[(Int, Array[Int])] or
DataSet[(Int, Array[(Int,Double)])] meaning (user, array of items), possibly
including the predicted scores as well. See [issue todo] for details.
Another question arising is whether to provide this function as a member of the
ALS class, as a switch-kind of parameter to the ALS implementation (meaning the
model is either a rating or a ranking recommender model) or in some other way.
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