23.1.2 An Illustrative Example
Let us look at a concrete example of Active Learning in a Recommender System.
This is only meant to demonstrate concepts, so it is oversimplified. Please note that
the similarity metric may differ depending on the method used; here, movies are
assumed to be close to one another if they belong to the same genre. Figure 23.1
shows two charts, the leftmost is our starting state, in which we have already asked
the user to rate a movie within the upper right group, which we will say is the SciFi genre. The right chart shows us four possibilities for selecting our next training
point: (a), (b), (c), or (d). If we select the training point (a) which is an obscure
movie (like The Goldfish Hunter), it does not affect our predictions because no
other movies (points) are nearby. If we select the training point (b), we can predict
the values for the points in the same area, but these predictions are already possible
from the training point in the same area (refer to the chart on the left). If training