Benchmark

import org.apache.mahout.math.DenseVector;
import org.apache.mahout.math.Vector;
import org.apache.mahout.math.function.IntObjectProcedure;
import org.apache.mahout.math.map.OpenIntObjectHashMap;

import java.util.Random;

public class Benchmark {

  static int NUM_FEATURES = 20;
  static Random RANDOM = new Random(0xdeadbeef);

  public static void main(String[] args) {

    int numItems = 2500000;
    OpenIntObjectHashMap<Vector> M = new OpenIntObjectHashMap<Vector>(numItems);

    for (int itemID = 0; itemID < numItems; itemID++) {
      M.put(itemID, randomVector(NUM_FEATURES));
    }

    int numUsers = 20;

    for (int n = 0; n < numUsers; n++) {

      final Vector userFeatures = randomVector(NUM_FEATURES);

      long start = System.currentTimeMillis();

      M.forEachPair(new IntObjectProcedure<Vector>() {
        @Override
        public boolean apply(int itemID, Vector itemFeatures) {
          userFeatures.dot(itemFeatures);
          return true;
        }
      });

      long pause = System.currentTimeMillis();

      M.forEachPair(new IntObjectProcedure<Vector>() {
        @Override
        public boolean apply(int itemID, Vector itemFeatures) {
          dot(userFeatures, itemFeatures);
          return true;
        }
      });

      long end = System.currentTimeMillis();

      System.out.println((pause - start) + " " + (end - pause));
    }


  }

  static double dot(Vector one, Vector two) {
    double sum = 0;
      for (int n = 0; n < NUM_FEATURES; n++) {
        sum += one.getQuick(n) * two.getQuick(n);
      }
    return sum;
  }

  static Vector randomVector(int size) {
    double[] values = new double[size];
    for (int n = 0; n < size; n++) {
      values[n] = RANDOM.nextDouble();
    }
    return new DenseVector(values, true);
  }

}

gistfile1.txt

Vector.dot() 832ms, direct dot 110ms
Vector.dot() 813ms, direct dot 96ms
Vector.dot() 650ms, direct dot 95ms
Vector.dot() 1584ms, direct dot 96ms
Vector.dot() 680ms, direct dot 105ms
Vector.dot() 728ms, direct dot 102ms
Vector.dot() 669ms, direct dot 102ms
Vector.dot() 669ms, direct dot 97ms
Vector.dot() 655ms, direct dot 98ms
Vector.dot() 668ms, direct dot 99ms
Vector.dot() 662ms, direct dot 116ms
Vector.dot() 671ms, direct dot 97ms
Vector.dot() 660ms, direct dot 96ms
Vector.dot() 649ms, direct dot 98ms
Vector.dot() 651ms, direct dot 96ms
Vector.dot() 670ms, direct dot 97ms
Vector.dot() 720ms, direct dot 98ms
Vector.dot() 653ms, direct dot 97ms
Vector.dot() 648ms, direct dot 97ms
Vector.dot() 662ms, direct dot 99ms