code: /*
   * Copyright 2015 recommenders.net.
   *
   * Licensed 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 net.recommenders.rival.core;
  
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Map;
  import java.util.Set;
  
  /**
   * Data model used throughout the toolkit. Able to store users, items,
   * preferences, timestamps.
   *
   * @author <a href="http://github.com/abellogin">Alejandro</a>, <a
   * href="http://github.com/alansaid">Alan</a>
   *
   * @param <U> generic type for users
   * @param <I> generic type for items
   */
  public class DataModel<U, I> implements DataModelIF<U, I> {
  
      /**
       * Preference map between users and items.
       */
      protected Map<U, Map<I, Double>> userItemPreferences;
      /**
       * Set containing all the items.
       */
      protected Set<I> items;
      /**
       * Flag to indicate if duplicate preferences should be ignored or not.
       * Default: false.
       */
      protected boolean ignoreDuplicatePreferences;
  
      /**
       * Default constructor.
       */
      DataModel() {
          this(false);
      }
  
      /**
       * Constructor with parameters.
       *
       * @param ignoreDupPreferences The flag to indicate whether preferences
       * should be ignored.
       */
      protected DataModel(final boolean ignoreDupPreferences) {
          this(ignoreDupPreferences, new HashMap<U, Map<I, Double>>(), new HashSet<I>());
      }
  
      /**
       * Constructor with parameters.
       *
       * @param ignoreDupPreferences The flag to indicate whether preferences
       * should be ignored.
       * @param userItemPreference The preference map between users and items.
       * @param itemSet The items.
       */
      protected DataModel(final boolean ignoreDupPreferences, final Map<U, Map<I, Double>> userItemPreference, final Set<I> itemSet) {
          this.ignoreDuplicatePreferences = ignoreDupPreferences;
          this.userItemPreferences = userItemPreference;
          this.items = itemSet;
      }
  
      /**
       * Method that returns the preference between a user and an item.
       *
       * @param u the user.
       * @param i the item.
       * @return the preference between a user and an item or NaN.
       */
      @Override
      public Double getUserItemPreference(U u, I i) {
          if (userItemPreferences.containsKey(u) && userItemPreferences.get(u).containsKey(i)) {
              return userItemPreferences.get(u).get(i);
          }
          return Double.NaN;
      }
  
      /**
       * Method that returns the items of a user.
       *
       * @param u the user.
       * @return the items of a user.
       */
      @Override
      public Iterable<I> getUserItems(U u) {
          if (userItemPreferences.containsKey(u)) {
              return userItemPreferences.get(u).keySet();
          }
          return Collections.emptySet();
      }
  
      /**
       * Method that adds a preference to the model between a user and an item.
       *
       * @param u the user.
       * @param i the item.
       * @param d the preference.
       */
      @Override
      public void addPreference(final U u, final I i, final Double d) {
          // update direct map
          Map<I, Double> userPreferences = userItemPreferences.get(u);
          if (userPreferences == null) {
              userPreferences = new HashMap<>();
              userItemPreferences.put(u, userPreferences);
          }
          Double preference = userPreferences.get(i);
          if (preference == null) {
              preference = 0.0;
          } else if (ignoreDuplicatePreferences) {
              // if duplicate preferences should be ignored, then we do not take into account the new value
              preference = null;
          }
          if (preference != null) {
              preference += d;
              userPreferences.put(i, preference);
          }
          // update items
          items.add(i);
      }
  
      /**
       * Method that returns the items in the model.
       *
       * @return the items in the model.
       */
      @Override
      public Iterable<I> getItems() {
          return items;
      }
  
      /**
       * Method that returns the users in the model.
       *
       * @return the users in the model.
       */
      @Override
      public Iterable<U> getUsers() {
          return userItemPreferences.keySet();
      }
  
      /**
       * Method that returns the number of items in the model.
       *
       * @return the number of items in the model.
       */
      @Override
      public int getNumItems() {
          return items.size();
      }
  
      /**
       * Method that returns the number of users in the model.
       *
       * @return the number of users in the model.
       */
      @Override
      public int getNumUsers() {
          return userItemPreferences.keySet().size();
      }
  
      /**
       * Method that clears all the maps contained in the model.
       */
      @Override
      public void clear() {
          userItemPreferences.clear();
          items.clear();
      }
  }
  