Hands-On Recommendation Systems with Python

The prediction problem

In this version of the problem, we are given a matrix of m users and n items. Each row of the matrix represents a user and each column represents an item. The value of the cell in the i^th row and the j^th column denotes the rating given by user i to item j. This value is usually denoted as r_ij.

For instance, consider the matrix in the following screenshot:

This matrix has seven users rating six items. Therefore, m = 7 and n = 6. User 1 has given the item 1 a rating of 4. Therefore, r₁₁ = 4.

Let us now consider a more concrete example. Imagine you are Netflix and you have a repository of 20,000 movies and 5,000 users. ...