/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.mahout.cf.taste.impl.recommender;
import org.apache.mahout.cf.taste.recommender.CandidateItemsStrategy;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.Callable;
import org.apache.mahout.cf.taste.common.Refreshable;
import org.apache.mahout.cf.taste.common.TasteException;
import org.apache.mahout.cf.taste.impl.common.FastIDSet;
import org.apache.mahout.cf.taste.impl.common.FullRunningAverage;
import org.apache.mahout.cf.taste.impl.common.RefreshHelper;
import org.apache.mahout.cf.taste.impl.common.RunningAverage;
import org.apache.mahout.cf.taste.model.DataModel;
import org.apache.mahout.cf.taste.model.PreferenceArray;
import org.apache.mahout.cf.taste.recommender.IDRescorer;
import org.apache.mahout.cf.taste.recommender.ItemBasedRecommender;
import org.apache.mahout.cf.taste.recommender.MostSimilarItemsCandidateItemsStrategy;
import org.apache.mahout.cf.taste.recommender.RecommendedItem;
import org.apache.mahout.cf.taste.recommender.Rescorer;
import org.apache.mahout.cf.taste.similarity.ItemSimilarity;
import org.apache.mahout.common.LongPair;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.google.common.base.Preconditions;
/**
* <p>
* A simple {@link org.apache.mahout.cf.taste.recommender.Recommender} which uses a given
* {@link org.apache.mahout.cf.taste.model.DataModel} and
* {@link org.apache.mahout.cf.taste.similarity.ItemSimilarity} to produce recommendations. This class
* represents Taste's support for item-based recommenders.
* </p>
*
* <p>
* The {@link org.apache.mahout.cf.taste.similarity.ItemSimilarity} is the most important point to discuss
* here. Item-based recommenders are useful because they can take advantage of something to be very fast: they
* base their computations on item similarity, not user similarity, and item similarity is relatively static.
* It can be precomputed, instead of re-computed in real time.
* </p>
*
* <p>
* Thus it's strongly recommended that you use
* {@link org.apache.mahout.cf.taste.impl.similarity.GenericItemSimilarity} with pre-computed similarities if
* you're going to use this class. You can use
* {@link org.apache.mahout.cf.taste.impl.similarity.PearsonCorrelationSimilarity} too, which computes
* similarities in real-time, but will probably find this painfully slow for large amounts of data.
* </p>
*/
public class GenericItemBasedRecommender extends AbstractRecommender implements ItemBasedRecommender {
private static final Logger log = LoggerFactory.getLogger(GenericItemBasedRecommender.class);
private final ItemSimilarity similarity;
private final MostSimilarItemsCandidateItemsStrategy mostSimilarItemsCandidateItemsStrategy;
private final RefreshHelper refreshHelper;
private EstimatedPreferenceCapper capper;
private static final boolean EXCLUDE_ITEM_IF_NOT_SIMILAR_TO_ALL_BY_DEFAULT = true;
public GenericItemBasedRecommender(DataModel dataModel,
ItemSimilarity similarity,
CandidateItemsStrategy candidateItemsStrategy,
MostSimilarItemsCandidateItemsStrategy mostSimilarItemsCandidateItemsStrategy) {
super(dataModel, candidateItemsStrategy);
Preconditions.checkArgument(similarity != null, "similarity is null");
this.similarity = similarity;
Preconditions.checkArgument(mostSimilarItemsCandidateItemsStrategy != null,
"mostSimilarItemsCandidateItemsStrategy is null");
this.mostSimilarItemsCandidateItemsStrategy = mostSimilarItemsCandidateItemsStrategy;
this.refreshHelper = new RefreshHelper(new Callable<Void>() {
@Override
public Void call() {
capper = buildCapper();
return null;
}
});
refreshHelper.addDependency(dataModel);
refreshHelper.addDependency(similarity);
refreshHelper.addDependency(candidateItemsStrategy);
refreshHelper.addDependency(mostSimilarItemsCandidateItemsStrategy);
capper = buildCapper();
}
public GenericItemBasedRecommender(DataModel dataModel, ItemSimilarity similarity) {
this(dataModel,
similarity,
AbstractRecommender.getDefaultCandidateItemsStrategy(),
getDefaultMostSimilarItemsCandidateItemsStrategy());
}
protected static MostSimilarItemsCandidateItemsStrategy getDefaultMostSimilarItemsCandidateItemsStrategy() {
return new PreferredItemsNeighborhoodCandidateItemsStrategy();
}
public ItemSimilarity getSimilarity() {
return similarity;
}
@Override
public List<RecommendedItem> recommend(long userID, int howMany, IDRescorer rescorer) throws TasteException {
Preconditions.checkArgument(howMany >= 1, "howMany must be at least 1");
log.debug("Recommending items for user ID '{}'", userID);
PreferenceArray preferencesFromUser = getDataModel().getPreferencesFromUser(userID);
if (preferencesFromUser.length() == 0) {
return Collections.emptyList();
}
FastIDSet possibleItemIDs = getAllOtherItems(userID, preferencesFromUser);
TopItems.Estimator<Long> estimator = new Estimator(userID, preferencesFromUser);
List<RecommendedItem> topItems = TopItems.getTopItems(howMany, possibleItemIDs.iterator(), rescorer,
estimator);
log.debug("Recommendations are: {}", topItems);
return topItems;
}
@Override
public float estimatePreference(long userID, long itemID) throws TasteException {
PreferenceArray preferencesFromUser = getDataModel().getPreferencesFromUser(userID);
Float actualPref = getPreferenceForItem(preferencesFromUser, itemID);
if (actualPref != null) {
return actualPref;
}
return doEstimatePreference(userID, preferencesFromUser, itemID);
}
private static Float getPreferenceForItem(PreferenceArray preferencesFromUser, long itemID) {
int size = preferencesFromUser.length();
for (int i = 0; i < size; i++) {
if (preferencesFromUser.getItemID(i) == itemID) {
return preferencesFromUser.getValue(i);
}
}
return null;
}
@Override
public List<RecommendedItem> mostSimilarItems(long itemID, int howMany) throws TasteException {
return mostSimilarItems(itemID, howMany, null);
}
@Override
public List<RecommendedItem> mostSimilarItems(long itemID, int howMany,
Rescorer<LongPair> rescorer) throws TasteException {
TopItems.Estimator<Long> estimator = new MostSimilarEstimator(itemID, similarity, rescorer);
return doMostSimilarItems(new long[] {itemID}, howMany, estimator);
}
@Override
public List<RecommendedItem> mostSimilarItems(long[] itemIDs, int howMany) throws TasteException {
TopItems.Estimator<Long> estimator = new MultiMostSimilarEstimator(itemIDs, similarity, null,
EXCLUDE_ITEM_IF_NOT_SIMILAR_TO_ALL_BY_DEFAULT);
return doMostSimilarItems(itemIDs, howMany, estimator);
}
@Override
public List<RecommendedItem> mostSimilarItems(long[] itemIDs, int howMany,
Rescorer<LongPair> rescorer) throws TasteException {
TopItems.Estimator<Long> estimator = new MultiMostSimilarEstimator(itemIDs, similarity, rescorer,
EXCLUDE_ITEM_IF_NOT_SIMILAR_TO_ALL_BY_DEFAULT);
return doMostSimilarItems(itemIDs, howMany, estimator);
}
@Override
public List<RecommendedItem> mostSimilarItems(long[] itemIDs,
int howMany,
boolean excludeItemIfNotSimilarToAll) throws TasteException {
TopItems.Estimator<Long> estimator = new MultiMostSimilarEstimator(itemIDs, similarity, null,
excludeItemIfNotSimilarToAll);
return doMostSimilarItems(itemIDs, howMany, estimator);
}
@Override
public List<RecommendedItem> mostSimilarItems(long[] itemIDs, int howMany,
Rescorer<LongPair> rescorer,
boolean excludeItemIfNotSimilarToAll) throws TasteException {
TopItems.Estimator<Long> estimator = new MultiMostSimilarEstimator(itemIDs, similarity, rescorer,
excludeItemIfNotSimilarToAll);
return doMostSimilarItems(itemIDs, howMany, estimator);
}
@Override
public List<RecommendedItem> recommendedBecause(long userID, long itemID, int howMany) throws TasteException {
Preconditions.checkArgument(howMany >= 1, "howMany must be at least 1");
DataModel model = getDataModel();
TopItems.Estimator<Long> estimator = new RecommendedBecauseEstimator(userID, itemID);
PreferenceArray prefs = model.getPreferencesFromUser(userID);
int size = prefs.length();
FastIDSet allUserItems = new FastIDSet(size);
for (int i = 0; i < size; i++) {
allUserItems.add(prefs.getItemID(i));
}
allUserItems.remove(itemID);
return TopItems.getTopItems(howMany, allUserItems.iterator(), null, estimator);
}
private List<RecommendedItem> doMostSimilarItems(long[] itemIDs,
int howMany,
TopItems.Estimator<Long> estimator) throws TasteException {
FastIDSet possibleItemIDs = mostSimilarItemsCandidateItemsStrategy.getCandidateItems(itemIDs, getDataModel());
return TopItems.getTopItems(howMany, possibleItemIDs.iterator(), null, estimator);
}
protected float doEstimatePreference(long userID, PreferenceArray preferencesFromUser, long itemID)
throws TasteException {
double preference = 0.0;
double totalSimilarity = 0.0;
int count = 0;
double[] similarities = similarity.itemSimilarities(itemID, preferencesFromUser.getIDs());
for (int i = 0; i < similarities.length; i++) {
double theSimilarity = similarities[i];
if (!Double.isNaN(theSimilarity)) {
// Weights can be negative!
preference += theSimilarity * preferencesFromUser.getValue(i);
totalSimilarity += theSimilarity;
count++;
}
}
// Throw out the estimate if it was based on no data points, of course, but also if based on
// just one. This is a bit of a band-aid on the 'stock' item-based algorithm for the moment.
// The reason is that in this case the estimate is, simply, the user's rating for one item
// that happened to have a defined similarity. The similarity score doesn't matter, and that
// seems like a bad situation.
if (count <= 1) {
return Float.NaN;
}
float estimate = (float) (preference / totalSimilarity);
if (capper != null) {
estimate = capper.capEstimate(estimate);
}
return estimate;
}
@Override
public void refresh(Collection<Refreshable> alreadyRefreshed) {
refreshHelper.refresh(alreadyRefreshed);
}
@Override
public String toString() {
return "GenericItemBasedRecommender[similarity:" + similarity + ']';
}
private EstimatedPreferenceCapper buildCapper() {
DataModel dataModel = getDataModel();
if (Float.isNaN(dataModel.getMinPreference()) && Float.isNaN(dataModel.getMaxPreference())) {
return null;
} else {
return new EstimatedPreferenceCapper(dataModel);
}
}
public static class MostSimilarEstimator implements TopItems.Estimator<Long> {
private final long toItemID;
private final ItemSimilarity similarity;
private final Rescorer<LongPair> rescorer;
public MostSimilarEstimator(long toItemID, ItemSimilarity similarity, Rescorer<LongPair> rescorer) {
this.toItemID = toItemID;
this.similarity = similarity;
this.rescorer = rescorer;
}
@Override
public double estimate(Long itemID) throws TasteException {
LongPair pair = new LongPair(toItemID, itemID);
if (rescorer != null && rescorer.isFiltered(pair)) {
return Double.NaN;
}
double originalEstimate = similarity.itemSimilarity(toItemID, itemID);
return rescorer == null ? originalEstimate : rescorer.rescore(pair, originalEstimate);
}
}
private final class Estimator implements TopItems.Estimator<Long> {
private final long userID;
private final PreferenceArray preferencesFromUser;
private Estimator(long userID, PreferenceArray preferencesFromUser) {
this.userID = userID;
this.preferencesFromUser = preferencesFromUser;
}
@Override
public double estimate(Long itemID) throws TasteException {
return doEstimatePreference(userID, preferencesFromUser, itemID);
}
}
private static final class MultiMostSimilarEstimator implements TopItems.Estimator<Long> {
private final long[] toItemIDs;
private final ItemSimilarity similarity;
private final Rescorer<LongPair> rescorer;
private final boolean excludeItemIfNotSimilarToAll;
private MultiMostSimilarEstimator(long[] toItemIDs, ItemSimilarity similarity, Rescorer<LongPair> rescorer,
boolean excludeItemIfNotSimilarToAll) {
this.toItemIDs = toItemIDs;
this.similarity = similarity;
this.rescorer = rescorer;
this.excludeItemIfNotSimilarToAll = excludeItemIfNotSimilarToAll;
}
@Override
public double estimate(Long itemID) throws TasteException {
RunningAverage average = new FullRunningAverage();
double[] similarities = similarity.itemSimilarities(itemID, toItemIDs);
for (int i = 0; i < toItemIDs.length; i++) {
long toItemID = toItemIDs[i];
LongPair pair = new LongPair(toItemID, itemID);
if (rescorer != null && rescorer.isFiltered(pair)) {
continue;
}
double estimate = similarities[i];
if (rescorer != null) {
estimate = rescorer.rescore(pair, estimate);
}
if (excludeItemIfNotSimilarToAll || !Double.isNaN(estimate)) {
average.addDatum(estimate);
}
}
double averageEstimate = average.getAverage();
return averageEstimate == 0 ? Double.NaN : averageEstimate;
}
}
private final class RecommendedBecauseEstimator implements TopItems.Estimator<Long> {
private final long userID;
private final long recommendedItemID;
private RecommendedBecauseEstimator(long userID, long recommendedItemID) {
this.userID = userID;
this.recommendedItemID = recommendedItemID;
}
@Override
public double estimate(Long itemID) throws TasteException {
Float pref = getDataModel().getPreferenceValue(userID, itemID);
if (pref == null) {
return Float.NaN;
}
double similarityValue = similarity.itemSimilarity(recommendedItemID, itemID);
return (1.0 + similarityValue) * pref;
}
}
}