@Override
protected void calculate(Dataset dataSet) {
int nUsers = dataSet.getUserCount();
similarityValues = new double[nUsers][nUsers];
// if we want to use mapping from userId to index then generate
// index for every userId
if (useObjIdToIndexMapping) {
for (User u : dataSet.getUsers()) {
idMapping.getIndex(String.valueOf(u.getId()));
}
}
for (int u = 0; u < nUsers; u++) {
int userAId = getObjIdFromIndex(u);
User userA = dataSet.getUser(userAId);
for (int v = u; v < nUsers; v++) {
int userBId = getObjIdFromIndex(v);
User userB = dataSet.getUser(userBId);
/* Collect shared ratings */
Integer[] sharedItemIds = User.getSharedItems(userA, userB);
if (sharedItemIds.length > 0) {
double[] ratingsA = userA.getRatingsForItemList(sharedItemIds);
double[] ratingsB = userB.getRatingsForItemList(sharedItemIds);
/* Center ratings by subtracting average */
double avgA = userA.getAverageRating();
double avgB = userB.getAverageRating();
for (int i = 0; i < sharedItemIds.length; i++) {
ratingsA[i] = ratingsA[i] - avgA;
ratingsB[i] = ratingsB[i] - avgB;
}
/* Calculate similarity - Pearson Correlation */
PearsonCorrelation pr = new PearsonCorrelation(ratingsA, ratingsB);
similarityValues[u][v] = pr.calculate();
} else {
similarityValues[u][v] = 0.0;
}
}
}
}
public MovieLensUserSimilarity(String id, Dataset ds) {
this.id = id;
this.useObjIdToIndexMapping = ds.isIdMappingRequired();
calculate(ds);
}