Tutorial: Build a Cypher Recommendation Engine

[adam_cowley]

We can now turn the co-actor query above into a recommendation query by following those relationships another step out to find the "co-co-actors", i.e. the second-degree actors in Tom’s network. This will show us all the actors Tom may not have worked with yet, and we can specify a criteria to be sure he hasn’t directly acted with that person.

MATCH (tom:Person {name: 'Tom Hanks'})-[:ACTED_IN]->(movie1:Movie)<-[:ACTED_IN]-(coActor:Person)-[:ACTED_IN]->(movie2:Movie)<-[:ACTED_IN]-(coCoActor:Person)
WHERE tom <> coCoActor
AND NOT (tom)-[:ACTED_IN]->(:Movie)<-[:ACTED_IN]-(coCoActor)
RETURN coCoActor.name

You probably noticed that a few names appear multiple times. This is because there are multiple paths to follow from Tom Hanks to these actors.

To see which co-co-actors appear most often in Tom’s network, we can take frequency of occurrences into account by counting the number of paths between Tom Hanks and each coCoActor and ordering them by highest to lowest value.

MATCH (tom:Person {name: 'Tom Hanks'})-[:ACTED_IN]->(movie1:Movie)<-[:ACTED_IN]-(coActor:Person)-[:ACTED_IN]->(movie2:Movie)<-[:ACTED_IN]-(coCoActor:Person)
WHERE tom <> coCoActor
AND NOT (tom)-[:ACTED_IN]->(:Movie)<-[:ACTED_IN]-(coCoActor)
RETURN coCoActor.name, count(coCoActor) as frequency
ORDER BY frequency DESC
LIMIT 5

One of those "co-co-actors" is Tom Cruise. Now let’s see which movies and actors are between the two Toms so we can find out who can introduce them.

Exploring the Paths

MATCH (tom:Person {name: 'Tom Hanks'})-[:ACTED_IN]->(movie1:Movie)<-[:ACTED_IN]-(coActor:Person)-[:ACTED_IN]->(movie2:Movie)<-[:ACTED_IN]-(cruise:Person {name: 'Tom Cruise'})
WHERE NOT (tom)-[:ACTED_IN]->(:Movie)<-[:ACTED_IN]-(cruise)
RETURN tom, movie1, coActor, movie2, cruise

As you can see, this returns multiple paths. If you have ever played the six degrees of Kevin Bacon game, this concept of seeing how many hops exist between people is exactly what graphs depict. You will notice that our results even return a path with Kevin Bacon himself.

With these two simple Cypher statements, we already created two recommendation algorithms - who to meet/work with next and how to meet them.

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This is a companion discussion topic for the original entry at https://neo4j.com/developer/cypher/guide-build-a-recommendation-engine/