hadoop WordStandardDeviation 源码

haddop WordStandardDeviation 代码

文件路径：/hadoop-mapreduce-project/hadoop-mapreduce-examples/src/main/java/org/apache/hadoop/examples/WordStandardDeviation.java

/**
 * 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.hadoop.examples;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

import org.apache.hadoop.thirdparty.com.google.common.base.Charsets;

public class WordStandardDeviation extends Configured implements Tool {

  private double stddev = 0;

  private final static Text LENGTH = new Text("length");
  private final static Text SQUARE = new Text("square");
  private final static Text COUNT = new Text("count");
  private final static LongWritable ONE = new LongWritable(1);

  /**
   * Maps words from line of text into 3 key-value pairs; one key-value pair for
   * counting the word, one for counting its length, and one for counting the
   * square of its length.
   */
  public static class WordStandardDeviationMapper extends
      Mapper<Object, Text, Text, LongWritable> {

    private LongWritable wordLen = new LongWritable();
    private LongWritable wordLenSq = new LongWritable();

    /**
     * Emits 3 key-value pairs for counting the word, its length, and the
     * squares of its length. Outputs are (Text, LongWritable).
     * 
     * @param value
     *          This will be a line of text coming in from our input file.
     */
    public void map(Object key, Text value, Context context)
        throws IOException, InterruptedException {
      StringTokenizer itr = new StringTokenizer(value.toString());
      while (itr.hasMoreTokens()) {
        String string = itr.nextToken();

        this.wordLen.set(string.length());

        // the square of an integer is an integer...
        this.wordLenSq.set((long) Math.pow(string.length(), 2.0));

        context.write(LENGTH, this.wordLen);
        context.write(SQUARE, this.wordLenSq);
        context.write(COUNT, ONE);
      }
    }
  }

  /**
   * Performs integer summation of all the values for each key.
   */
  public static class WordStandardDeviationReducer extends
      Reducer<Text, LongWritable, Text, LongWritable> {

    private LongWritable val = new LongWritable();

    /**
     * Sums all the individual values within the iterator and writes them to the
     * same key.
     * 
     * @param key
     *          This will be one of 2 constants: LENGTH_STR, COUNT_STR, or
     *          SQUARE_STR.
     * @param values
     *          This will be an iterator of all the values associated with that
     *          key.
     */
    public void reduce(Text key, Iterable<LongWritable> values, Context context)
        throws IOException, InterruptedException {

      int sum = 0;
      for (LongWritable value : values) {
        sum += value.get();
      }
      val.set(sum);
      context.write(key, val);
    }
  }

  /**
   * Reads the output file and parses the summation of lengths, the word count,
   * and the lengths squared, to perform a quick calculation of the standard
   * deviation.
   * 
   * @param path
   *          The path to find the output file in. Set in main to the output
   *          directory.
   * @throws IOException
   *           If it cannot access the output directory, we throw an exception.
   */
  private double readAndCalcStdDev(Path path, Configuration conf)
      throws IOException {
    FileSystem fs = FileSystem.get(conf);
    Path file = new Path(path, "part-r-00000");

    if (!fs.exists(file))
      throw new IOException("Output not found!");

    double stddev = 0;
    BufferedReader br = null;
    try {
      br = new BufferedReader(new InputStreamReader(fs.open(file), Charsets.UTF_8));
      long count = 0;
      long length = 0;
      long square = 0;
      String line;
      while ((line = br.readLine()) != null) {
        StringTokenizer st = new StringTokenizer(line);

        // grab type
        String type = st.nextToken();

        // differentiate
        if (type.equals(COUNT.toString())) {
          String countLit = st.nextToken();
          count = Long.parseLong(countLit);
        } else if (type.equals(LENGTH.toString())) {
          String lengthLit = st.nextToken();
          length = Long.parseLong(lengthLit);
        } else if (type.equals(SQUARE.toString())) {
          String squareLit = st.nextToken();
          square = Long.parseLong(squareLit);
        }
      }
      // average = total sum / number of elements;
      double mean = (((double) length) / ((double) count));
      // standard deviation = sqrt((sum(lengths ^ 2)/count) - (mean ^ 2))
      mean = Math.pow(mean, 2.0);
      double term = (((double) square / ((double) count)));
      stddev = Math.sqrt((term - mean));
      System.out.println("The standard deviation is: " + stddev);
    } finally {
      if (br != null) {
        br.close();
      }
    }
    return stddev;
  }

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

  @Override
  public int run(String[] args) throws Exception {
    if (args.length != 2) {
      System.err.println("Usage: wordstddev <in> <out>");
      return 0;
    }

    Configuration conf = getConf();

    Job job = Job.getInstance(conf, "word stddev");
    job.setJarByClass(WordStandardDeviation.class);
    job.setMapperClass(WordStandardDeviationMapper.class);
    job.setCombinerClass(WordStandardDeviationReducer.class);
    job.setReducerClass(WordStandardDeviationReducer.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(LongWritable.class);
    FileInputFormat.addInputPath(job, new Path(args[0]));
    Path outputpath = new Path(args[1]);
    FileOutputFormat.setOutputPath(job, outputpath);
    boolean result = job.waitForCompletion(true);

    // read output and calculate standard deviation
    stddev = readAndCalcStdDev(outputpath, conf);

    return (result ? 0 : 1);
  }

  public double getStandardDeviation() {
    return stddev;
  }
}

相关信息

hadoop 源码目录

相关文章

hadoop AggregateWordCount 源码

hadoop AggregateWordHistogram 源码

hadoop BaileyBorweinPlouffe 源码

hadoop DBCountPageView 源码

hadoop ExampleDriver 源码

hadoop Grep 源码

hadoop Join 源码

hadoop MultiFileWordCount 源码

hadoop QuasiMonteCarlo 源码

hadoop RandomTextWriter 源码