org.apache.mahout.classifier.naivebayes.training.ThetaMapper Maven / Gradle / Ivy

/**
 * 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.classifier.naivebayes.training;

import java.io.IOException;
import java.util.Map;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.mahout.classifier.naivebayes.BayesUtils;
import org.apache.mahout.math.Vector;
import org.apache.mahout.math.VectorWritable;

public class ThetaMapper extends Mapper {

  public static final String ALPHA_I = ThetaMapper.class.getName() + ".alphaI";
  static final String TRAIN_COMPLEMENTARY = ThetaMapper.class.getName() + ".trainComplementary";

  private ComplementaryThetaTrainer trainer;

  @Override
  protected void setup(Context ctx) throws IOException, InterruptedException {
    super.setup(ctx);
    Configuration conf = ctx.getConfiguration();

    float alphaI = conf.getFloat(ALPHA_I, 1.0f);
    Map scores = BayesUtils.readScoresFromCache(conf);    
    
    trainer = new ComplementaryThetaTrainer(scores.get(TrainNaiveBayesJob.WEIGHTS_PER_FEATURE),
                                            scores.get(TrainNaiveBayesJob.WEIGHTS_PER_LABEL), alphaI);
  }

  @Override
  protected void map(IntWritable key, VectorWritable value, Context ctx) throws IOException, InterruptedException {
    trainer.train(key.get(), value.get());
  }

  @Override
  protected void cleanup(Context ctx) throws IOException, InterruptedException {
    ctx.write(new Text(TrainNaiveBayesJob.LABEL_THETA_NORMALIZER),
        new VectorWritable(trainer.retrievePerLabelThetaNormalizer()));
    super.cleanup(ctx);
  }
}