redpoll.text.TfIdfMapper.java Source code

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Here is the source code for redpoll.text.TfIdfMapper.java

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/** 
 * 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 redpoll.text;

import java.io.IOException;
import java.util.HashMap;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.io.DefaultStringifier;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.MapReduceBase;
import org.apache.hadoop.mapred.Mapper;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.util.GenericsUtil;

/**
 * Mapper to create vsm of documents.
 * @author Jeremy Chow(coderplay@gmail.com)
 */
public class TfIdfMapper extends MapReduceBase implements Mapper<Text, TfArrayWritable, Text, TfIdfWritable> {
    private static final Log log = LogFactory.getLog(TfIdfMapper.class.getName());

    private HashMap<String, Integer> terms = null;
    private int toalDocNum;

    public void map(Text key, TfArrayWritable value, OutputCollector<Text, TfIdfWritable> output, Reporter reporter)
            throws IOException {
        Writable[] tfs = value.get();
        double df = (double) tfs.length; // document frequcy
        Integer index = terms.get(key.toString()); // index of term vector

        for (int i = 0; i < tfs.length; i++) {
            TfWritable tfWritable = (TfWritable) tfs[i];
            double tf = 1.0 + Math.log(1.0 + Math.log((double) tfWritable.getTf()));
            double idf = Math.log((1 + toalDocNum) / df);
            double tfIdf = tf * idf;

            output.collect(new Text(tfWritable.getDocumentId()),
                    new TfIdfWritable(new ElementWritable(index.intValue(), tfIdf)));
        }
    }

    @Override
    public void configure(JobConf job) {
        try {
            terms = new HashMap<String, Integer>();

            DefaultStringifier<HashMap<String, Integer>> mapStringifier = new DefaultStringifier<HashMap<String, Integer>>(
                    job, GenericsUtil.getClass(terms));

            String docFreqString = job.get("redpoll.text.terms");
            terms = mapStringifier.fromString(docFreqString);
            toalDocNum = job.getInt("redpoll.docs.num", 1024);
        } catch (IOException exp) {
            exp.printStackTrace();
        }
    }
}