mahout系列----minhash聚类

Map:

Vector featureVector = features.get();

if (featureVector.size() < minVectorSize) {

      return;

    }

    // Initialize the MinHash values to highest

    for (int i = 0; i < numHashFunctions; i++) {

      minHashValues[i] = Integer.MAX_VALUE;

    }



    for (int i = 0; i < numHashFunctions; i++) {

      for (Vector.Element ele : featureVector.nonZeroes()) {

        int value = hashValue ? (int) ele.get() : ele.index();

        bytesToHash[0] = (byte) (value >> 24);

        bytesToHash[1] = (byte) (value >> 16);

        bytesToHash[2] = (byte) (value >> 8);

        bytesToHash[3] = (byte) value;

        int hashIndex = hashFunction[i].hash(bytesToHash);

        //if our new hash value is less than the old one, replace the old one

        if (minHashValues[i] > hashIndex) {

          minHashValues[i] = hashIndex;

        }

      }

    }

    // output the cluster information

    for (int i = 0; i < numHashFunctions; i++) {

      StringBuilder clusterIdBuilder = new StringBuilder();

      for (int j = 0; j < keyGroups; j++) {

        clusterIdBuilder.append(minHashValues[(i + j) % numHashFunctions]).append('-');

      }

      //remove the last dash

      clusterIdBuilder.deleteCharAt(clusterIdBuilder.length() - 1);



      cluster.set(clusterIdBuilder.toString());



      if (debugOutput) {

        vector.set(featureVector);

        context.write(cluster, vector);

      } else {

        context.write(cluster, item);

      }

    }

 protected void reduce(Text cluster, Iterable<Writable> points, Context context)

    throws IOException, InterruptedException {

    Collection<Writable> pointList = Lists.newArrayList();

    for (Writable point : points) {

      if (debugOutput) {

        Vector pointVector = ((VectorWritable) point).get().clone();

        Writable writablePointVector = new VectorWritable(pointVector);

        pointList.add(writablePointVector);

      } else {

        Writable pointText = new Text(point.toString());

        pointList.add(pointText);

      }

    }

    if (pointList.size() >= minClusterSize) {

      context.getCounter(Clusters.ACCEPTED).increment(1);

      for (Writable point : pointList) {

        context.write(cluster, point);

      }

    } else {

      context.getCounter(Clusters.DISCARDED).increment(1);

    }

  }