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Optional components of Mahout which generally support interaction with third party systems, formats, APIs, etc.
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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 org.apache.mahout.utils.vectors;

import java.util.List;
import java.util.Map;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.util.ToolRunner;
import org.apache.mahout.common.AbstractJob;
import org.apache.mahout.common.Pair;
import org.apache.mahout.common.iterator.sequencefile.PathFilters;
import org.apache.mahout.common.iterator.sequencefile.PathType;
import org.apache.mahout.common.iterator.sequencefile.SequenceFileDirIterable;
import org.apache.mahout.math.VectorWritable;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Converts a vector representation of documents into a {@code document x terms} matrix.
 * The input data is in {@code SequenceFile} format (as generated by
 * {@link org.apache.mahout.vectorizer.SparseVectorsFromSequenceFiles SparseVectorsFromSequenceFiles}
 * or by {@link org.apache.mahout.vectorizer.EncodedVectorsFromSequenceFiles EncodedVectorsFromSequenceFiles})
 * and generates the following two files as output:
 * 
A file called "matrix" of format {@code SequenceFile}.
 * A file called "docIndex" of format {@code SequenceFile}.
 * The input file can be regenerated by joining the two output files on the generated int key.
 * In other words, {@code RowIdJob} replaces the document text ids by integers.
 * The original document text ids can still be retrieved from the "docIndex".
 */
public class RowIdJob extends AbstractJob {
  private static final Logger log = LoggerFactory.getLogger(RowIdJob.class);

  @Override
  public int run(String[] args) throws Exception {

    addInputOption();
    addOutputOption();

    Map> parsedArgs = parseArguments(args);
    if (parsedArgs == null) {
      return -1;
    }

    Configuration conf = getConf();
    FileSystem fs = FileSystem.get(conf);

    Path outputPath = getOutputPath();
    Path indexPath = new Path(outputPath, "docIndex");
    Path matrixPath = new Path(outputPath, "matrix");

    try (SequenceFile.Writer indexWriter = SequenceFile.createWriter(fs, conf, indexPath,
        IntWritable.class, Text.class);
         SequenceFile.Writer matrixWriter = SequenceFile.createWriter(fs, conf, matrixPath, IntWritable.class,
             VectorWritable.class)) {
      IntWritable docId = new IntWritable();
      int i = 0;
      int numCols = 0;
      for (Pair record
          : new SequenceFileDirIterable(getInputPath(), PathType.LIST, PathFilters.logsCRCFilter(),
          null, true, conf)) {
        VectorWritable value = record.getSecond();
        docId.set(i);
        indexWriter.append(docId, record.getFirst());
        matrixWriter.append(docId, value);
        i++;
        numCols = value.get().size();
      }

      log.info("Wrote out matrix with {} rows and {} columns to {}", i, numCols, matrixPath);
      return 0;
    }
  }

  public static void main(String[] args) throws Exception {
    ToolRunner.run(new RowIdJob(), args);
  }

}