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The Universal Recommender

The Universal Recommender (UR) is a new type of collaborative filtering recommender based on an algorithm that can use data from a wide variety of user taste indicators—it uses the Correlated Cross-Occurrence algorithm (CCO). Unlike the matrix factorization embodied in things like MLlib's ALS, The UR's CCO algorithm is able to ingest any number of user actions, events, profile data, and contextual information. It then serves results in a fast and scalable way. It also supports item properties for filtering and boosting recommendations and can therefor be considered a hybrid collaborative filtering and content-based recommender.

The use of multiple types of data fundamentally changes the way a recommender is used and, when employed correctly, will provide a significant increase in quality of recommendations vs. using only one "conversion event". Most recommenders, for instance, can only use one indicator of user taste a "purchase" event. Using all we know about a user and their context allows us to much better predict their preferences.

Not only does this data give lift to recommendation quality but it allows users who have little or no conversions to get recommendations. Therefore is can be used in places where conversions not as common. It also allows us to enrich preference indicators by extracting entities for text or learning topics and inferring preferences when users read something from a topic.

Even though this may sound complex, the Universal Recommender can be used well in more typical cases with no complex setup.

Quick Start

For the impatient head to the quickstart and be aware that the UR requires Apache PredictionIO with Elasticsearch. You are free to pick any backing data store but make sure Elasticsearch is installed.

Typical Uses:

There is a reason we call this recommender "universal" and it's because of the number of use cases it can be applied to.

Simple Configuration

All of the above use cases can be very simple to configure and setup. If you have an E-Commerce application, you may be able to get away with one type of input data and some item properties to get all of the benefits. If you have more complex needs, read the Use Cases section for tips.

The Correlated Cross-Occurrence Algorithm (CCO)

For most of the history of recommenders the data science could only find ways to use one type in user-preference indicator. To be sure this was one type per application but there is so much more we know from user behavior that was going unused. Correlated Cross-Occurrence (CCO) was developed to discover what behavior of a give user correlated to the type of action you want to recommend. If you want to recommend buy, play, watch, or read, is it possible that other things known about a user correlates to this recommended action—things like a pageview, a like, a category preference, the location logged in from, the device used, item detail views, or anything else known about the user. Furthermore how would we test for correlation?

Enter the Log-Likelihood Ratio (LLR)—a probabilistic test for correlation between 2 events. This is super important because there is no linear relationship between the event-types. The correlation is at the indiviual user and event level and this is where LLR excels. To illustrate this ask yourself in an E-commerce situation is a product view 1/2 of a buy? You might think so but if the user viewed 2 things and bought one of them the correlation is 100% for one of the views and 0% for the other. So some view data is useful in predicting purchases and others are useless. LLR is a very well respected test for this type of correlation.