Regression and Classification The problem of predicting a user’s ratings could be
treated as both a regression and a classification problem. It is a regression problem
since the ratings are discrete numerical values, such as if we consider their ordinal properties, meaning the ratings could be ordered (e.g. a rating of 4 is higher
than a rating of 3). On the other hand, we can disregard the numerical properties
of the ratings and treat the problem as a classification one by treating ratings as
classes/labels.6 For example, we can use a nearest-neighbor (NN) approach to do
classification, e.g. pick the most frequent label of the neighbors; or we can use NN
to do regression, e.g. calculate the mean of the ratings of the neighbors. Throughout