private double doItemSimilarity(long itemID1, long itemID2, FastIDSet preferring1)
throws TasteException {
double intersection = 0.0;
double union = 0.0;
for (Preference pref : getDataModel().getPreferencesForItem(itemID2)) {
long userID = pref.getUserID();
double weight = (double) getDataModel().getNumItems() / mUserPrefNum.get(userID);
if (preferring1.contains(userID)) {
intersection += weight;
union -= weight;
}
union += weight;
}
for (LongPrimitiveIterator it_user = preferring1.iterator(); it_user.hasNext(); ) {
long userID = (long) it_user.nextLong();
double weight = (double) getDataModel().getNumItems() / mUserPrefNum.get(userID);
union += weight;
}
if (intersection == 0) {
return Double.NaN;
}
return Math.log(intersection) / Math.log(union);
}
private FastIDSet toUserFastIDSet(PreferenceArray array) {
FastIDSet fastIDSet = new FastIDSet();
for (Preference preference : array) {
fastIDSet.add(preference.getUserID());
}
return fastIDSet;
}