Collaborative filtering is based on the idea that, somewhere out there in the world, you have a taste doppelganger—someone who shares the same notions about how good Star Wars is and how awful Love Actually is.
The idea is that you've rated some set of items in a way that's very similar to the way this other person, this doppelganger, has rated them, but then each of you has rated additional items that the other hasn't. Because you've established that your tastes are similar, recommendations can be generated from the items your doppelganger has rated highly but which you haven't rated and vice versa. It's in a way much like digital matchmaking, but with the outcome being songs or products you would like, ...
