# Embeddings: Motivation From Collaborative Filtering

Collaborative filtering is the task of making predictions about the interests of a user based on interests of many other users. As an example, let's look at the task of movie recommendation. Suppose we have 500,000 users, and a list of the movies each user has watched (from a catalog of 1,000,000 movies). Our goal is to recommend movies to users.

To solve this problem some method is needed to determine which movies are similar to each other. We can achieve this goal by embedding the movies into a low-dimensional space created such that similar movies are nearby.

Before describing how we can learn the embedding, we first explore the type of qualities we want the embedding to have, and how we will represent the training data for learning the embedding.

## Arrange Movies on a One-Dimensional Number Line

To help develop intuition about embeddings, on a piece of paper, try to arrange the following movies on a one-dimensional number line so that the movies nearest each other are the most closely related:

Movie Rating Description
Bleu R A French widow grieves the loss of her husband and daughter after they perish in a car accident.
The Dark Knight Rises PG-13 Batman endeavors to save Gotham City from nuclear annihilation in this sequel to The Dark Knight, set in the DC Comics universe.
Harry Potter and the Sorcerer's Stone PG A orphaned boy discovers he is a wizard and enrolls in Hogwarts School of Witchcraft and Wizardry, where he wages his first battle against the evil Lord Voldemort.
The Incredibles PG A family of superheroes forced to live as civilians in suburbia come out of retirement to save the superhero race from Syndrome and his killer robot.
Shrek PG A lovable ogre and his donkey sidekick set off on a mission to rescue Princess Fiona, who is emprisoned in her castle by a dragon.
Star Wars PG Luke Skywalker and Han Solo team up with two androids to rescue Princess Leia and save the galaxy.
The Triplets of Belleville PG-13 When professional cycler Champion is kidnapped during the Tour de France, his grandmother and overweight dog journey overseas to rescue him, with the help of a trio of elderly jazz singers.
Memento R An amnesiac desperately seeks to solve his wife's murder by tattooing clues onto his body.

## Arrange Movies in a Two-Dimensional Space

Try the same exercise as before, but this time arrange the same movies in a two-dimensional space.

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