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);
   }
 }

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