/**
* Gets the most recently added item not rated yet (new item in the platform).
*
* @return The most recently added item not rated yet.
*/
public Long getLastItemAddedNotRated() {
Long lastItemAdded = null;
Date threshold = null;
for (Long itemId : idao.getItemIds()) {
List<Rating> ratings = iedao.getEventsForItem(itemId, Rating.class);
Date firstTimestamp = new Date(ratings.get(0).getTimestamp() * 1000);
if (threshold == null) {
threshold = firstTimestamp;
lastItemAdded = itemId;
}
for (Rating r : ratings) {
Date timestamp = new Date(r.getTimestamp() * 1000);
if (timestamp.before(firstTimestamp)) firstTimestamp = timestamp;
}
if (firstTimestamp.after(threshold)) {
threshold = firstTimestamp;
lastItemAdded = itemId;
}
}
return lastItemAdded;
}
/**
* Build the SVD model.
*
* @return A singular value decomposition recommender model.
*/
@Override
public SVDModel get() {
// Create index mappings of user and item IDs.
// You can use these to find row and columns in the matrix based on user/item IDs.
IdIndexMapping userMapping = IdIndexMapping.create(userDAO.getUserIds());
logger.debug("indexed {} users", userMapping.size());
IdIndexMapping itemMapping = IdIndexMapping.create(itemDAO.getItemIds());
logger.debug("indexed {} items", itemMapping.size());
// We have to do 2 things:
// First, prepare a matrix containing the rating data.
RealMatrix matrix = createRatingMatrix(userMapping, itemMapping);
// Second, compute its factorization
// All the work is done in the constructor
SingularValueDecomposition svd = new SingularValueDecomposition(matrix);
// Third, truncate the decomposed matrix
// TODO Truncate the matrices and construct the SVD model
RealMatrix userMatrix = svd.getU();
RealMatrix weights = svd.getS();
RealMatrix itemMatrix = svd.getV();
userMatrix = userMatrix.getSubMatrix(0, userMatrix.getRowDimension() - 1, 0, featureCount - 1);
weights = weights.getSubMatrix(0, featureCount - 1, 0, featureCount - 1);
itemMatrix = itemMatrix.getSubMatrix(0, itemMatrix.getRowDimension() - 1, 0, featureCount - 1);
return new SVDModel(userMapping, itemMapping, userMatrix, itemMatrix, weights);
}
/**
* Gets the most popular item, i.e. the item with the greatest number of ratings, in a certain
* period of time (last week/month/year/ever).
*
* @param period Period of time to consider.
* @return The most popular item.
*/
@SuppressWarnings("deprecation")
public Long getMostPopularItem(Period period) {
Calendar cal = Calendar.getInstance();
cal.setTime(getLastTimestamp());
Date thresholdDate = null;
switch (period) {
case LAST_WEEK:
cal.add(Calendar.DATE, -7);
thresholdDate = cal.getTime();
break;
case LAST_MONTH:
cal.add(Calendar.DATE, -30);
thresholdDate = cal.getTime();
break;
case LAST_YEAR:
cal.add(Calendar.DATE, -365);
thresholdDate = cal.getTime();
break;
case EVER:
break;
}
Long idItemMostPopular = null;
int max = 0;
for (Long itemId : idao.getItemIds()) {
List<Event> events = iedao.getEventsForItem(itemId);
int count = 0;
if (thresholdDate == null) count = events.size();
else {
thresholdDate.setHours(0);
thresholdDate.setMinutes(0);
thresholdDate.setSeconds(0);
for (Event ev : events) {
Date rateDate = new Date(ev.getTimestamp() * 1000);
if (rateDate.after(thresholdDate)) count++;
}
}
if (count > max) {
idItemMostPopular = itemId;
max = count;
}
}
return idItemMostPopular;
}
/**
* Gets the last positively rated item (the last item added in the platform rated in a positive
* way). An item is "positively rated" if its rate is equals or greater than the global mean of
* all ratings.
*
* @return The last positively rated item.
*/
public Long getLastPositivelyRatedItem() {
Long lastPositivelyRatedItem = null;
Date recentDate = getFirstTimestamp();
for (Long itemId : idao.getItemIds()) {
List<Rating> ratings = iedao.getEventsForItem(itemId, Rating.class);
int threshold = getPositiveRatingThreshold(ratings);
Date date = getFirstTimestamp();
for (Rating rating : ratings) {
Date dateR = new Date(rating.getTimestamp() * 1000);
if (rating.getValue() >= threshold && dateR.after(date)) date = dateR;
}
if (date.after(recentDate)) recentDate = date;
lastPositivelyRatedItem = itemId;
}
return lastPositivelyRatedItem;
}