GenderItemSimilarity.java

/*
 * Source code for listing 5.2
 * 
 */
package mia.recommender.ch05;

import org.apache.mahout.cf.taste.common.Refreshable;
import org.apache.mahout.cf.taste.impl.common.FastIDSet;
import org.apache.mahout.cf.taste.similarity.ItemSimilarity;

import java.util.Collection;

public class GenderItemSimilarity implements ItemSimilarity {

  private final FastIDSet men;
  private final FastIDSet women;

  public GenderItemSimilarity(FastIDSet men, FastIDSet women) {
    this.men = men;
    this.women = women;
  }

  @Override
  public double itemSimilarity(long profileID1, long profileID2) {
    Boolean profile1IsMan = isMan(profileID1);
    if (profile1IsMan == null) {
      return 0.0;
    }
    Boolean profile2IsMan = isMan(profileID2);
    if (profile2IsMan == null) {
      return 0.0;
    }
    return profile1IsMan == profile2IsMan ? 1.0 : -1.0;
  }

  @Override
  public double[] itemSimilarities(long itemID1, long[] itemID2s) {
    double[] result = new double[itemID2s.length];
    for (int i = 0; i < itemID2s.length; i++) {
      result[i] = itemSimilarity(itemID1, itemID2s[i]);
    }
    return result;
  }

  @Override
  public long[] allSimilarItemIDs(long itemID) {
    throw new UnsupportedOperationException();
  }

  private Boolean isMan(long profileID) {
    if (men.contains(profileID)) {
      return Boolean.TRUE;
    }
    if (women.contains(profileID)) {
      return Boolean.FALSE;
    }
    return null;
  }

  @Override
  public void refresh(Collection<Refreshable> alreadyRefreshed) {
    // do nothing
  }

}