/**
* Calculates the weight for two users over all items they share recorded ratings for.
*
* @param train User object for particular user in training data.
* @param test User object for active user.
* @return Returns a Double representing the computed weight.
*/
public static double calculateWeight(User train, User test) {
double numSum = 0;
double denTestSum = 0;
double denTrainSum = 0;
Map<Integer, Rating> ratings = train.getRatings();
for (Rating r : test.getRatings().values()) {
if (ratings.containsKey(r.getMovieId())) {
numSum +=
(r.getRating() - test.getMean())
* (ratings.get(r.getMovieId()).getRating() - train.getMean());
denTestSum += Math.pow(r.getRating() - test.getMean(), 2);
denTrainSum += Math.pow(ratings.get(r.getMovieId()).getRating() - train.getMean(), 2);
}
}
return (denTestSum == 0 || denTrainSum == 0) ? 0 : numSum / Math.sqrt(denTestSum * denTrainSum);
}
