/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.mahout.clustering.minhash;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.mahout.clustering.minhash.HashFactory.HashType;
import org.apache.mahout.common.commandline.MinhashOptionCreator;
import org.apache.mahout.math.Vector;
import org.apache.mahout.math.VectorWritable;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.IOException;
public class MinHashMapper extends Mapper<Text, VectorWritable, Text, Writable> {
private static final Logger log = LoggerFactory.getLogger(MinHashMapper.class);
private HashFunction[] hashFunction;
private int numHashFunctions;
private int keyGroups;
private int minVectorSize;
private boolean debugOutput;
private int[] minHashValues;
private byte[] bytesToHash;
@Override
protected void setup(Context context) throws IOException, InterruptedException {
super.setup(context);
Configuration conf = context.getConfiguration();
this.numHashFunctions = conf.getInt(MinhashOptionCreator.NUM_HASH_FUNCTIONS, 10);
this.minHashValues = new int[numHashFunctions];
this.bytesToHash = new byte[4];
this.keyGroups = conf.getInt(MinhashOptionCreator.KEY_GROUPS, 1);
this.minVectorSize = conf.getInt(MinhashOptionCreator.MIN_VECTOR_SIZE, 5);
String htype = conf.get(MinhashOptionCreator.HASH_TYPE, "linear");
this.debugOutput = conf.getBoolean(MinhashOptionCreator.DEBUG_OUTPUT, false);
HashType hashType;
try {
hashType = HashType.valueOf(htype);
} catch (IllegalArgumentException iae) {
log.warn("No valid hash type found in configuration for {}, assuming type: {}", htype, HashType.LINEAR);
hashType = HashType.LINEAR;
}
hashFunction = HashFactory.createHashFunctions(hashType, numHashFunctions);
}
/**
* Hash all items with each function and retain min. value for each iteration. We up with X number of
* minhash signatures.
* <p/>
* Now depending upon the number of key-groups (1 - 4) concatenate that many minhash values to form
* cluster-id as 'key' and item-id as 'value'
*/
@Override
public void map(Text item, VectorWritable features, Context context) throws IOException, InterruptedException {
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) {
int value = (int) ele.get();
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);
Text cluster = new Text(clusterIdBuilder.toString());
Writable point;
if (debugOutput) {
point = new VectorWritable(featureVector.clone());
} else {
point = new Text(item.toString());
}
context.write(cluster, point);
}
}
}