MAPREDUCE-2669. Add new examples for Mean, Median, and Standard Deviation. Contributed by Plamen Jeliazkov.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1169874 13f79535-47bb-0310-9956-ffa450edef68

hadoop-mapreduce-project/CHANGES.txt

@@ -2,6 +2,13 @@ Hadoop MapReduce Change Log
 
 Trunk (unreleased changes)
 
+  INCOMPATIBLE CHANGES
+
+  NEW FEATURES
+
+    MAPREDUCE-2669. Add new examples for Mean, Median, and Standard Deviation.
+    (Plamen Jeliazkov via shv)
+
   IMPROVEMENTS
 
     MAPREDUCE-2887 due to HADOOP-7524 Change RPC to allow multiple protocols

hadoop-mapreduce-project/src/examples/org/apache/hadoop/examples/WordMean.java

@@ -0,0 +1,196 @@
+package org.apache.hadoop.examples;
+
+/**
+ * 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.
+ */
+
+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;
+
+public class WordMean extends Configured implements Tool {
+
+  private double mean = 0;
+
+  private final static Text COUNT = new Text("count");
+  private final static Text LENGTH = new Text("length");
+  private final static LongWritable ONE = new LongWritable(1);
+
+  /**
+   * Maps words from line of text into 2 key-value pairs; one key-value pair for
+   * counting the word, another for counting its length.
+   */
+  public static class WordMeanMapper extends
+      Mapper<Object, Text, Text, LongWritable> {
+
+    private LongWritable wordLen = new LongWritable();
+
+    /**
+     * Emits 2 key-value pairs for counting the word and 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());
+        context.write(LENGTH, this.wordLen);
+        context.write(COUNT, ONE);
+      }
+    }
+  }
+
+  /**
+   * Performs integer summation of all the values for each key.
+   */
+  public static class WordMeanReducer extends
+      Reducer<Text, LongWritable, Text, LongWritable> {
+
+    private LongWritable sum = 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 or COUNT_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 theSum = 0;
+      for (LongWritable val : values) {
+        theSum += val.get();
+      }
+      sum.set(theSum);
+      context.write(key, sum);
+    }
+  }
+
+  /**
+   * Reads the output file and parses the summation of lengths, and the word
+   * count, to perform a quick calculation of the mean.
+   * 
+   * @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 readAndCalcMean(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!");
+
+    BufferedReader br = null;
+
+    // average = total sum / number of elements;
+    try {
+      br = new BufferedReader(new InputStreamReader(fs.open(file)));
+
+      long count = 0;
+      long length = 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);
+        }
+      }
+
+      double theMean = (((double) length) / ((double) count));
+      System.out.println("The mean is: " + theMean);
+      return theMean;
+    } finally {
+      br.close();
+    }
+  }
+
+  public static void main(String[] args) throws Exception {
+    ToolRunner.run(new Configuration(), new WordMean(), args);
+  }
+
+  @Override
+  public int run(String[] args) throws Exception {
+    if (args.length != 2) {
+      System.err.println("Usage: wordmean <in> <out>");
+      return 0;
+    }
+
+    Configuration conf = getConf();
+
+    @SuppressWarnings("deprecation")
+    Job job = new Job(conf, "word mean");
+    job.setJarByClass(WordMean.class);
+    job.setMapperClass(WordMeanMapper.class);
+    job.setCombinerClass(WordMeanReducer.class);
+    job.setReducerClass(WordMeanReducer.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);
+    mean = readAndCalcMean(outputpath, conf);
+
+    return (result ? 0 : 1);
+  }
+
+  /**
+   * Only valuable after run() called.
+   * 
+   * @return Returns the mean value.
+   */
+  public double getMean() {
+    return mean;
+  }
+}

hadoop-mapreduce-project/src/examples/org/apache/hadoop/examples/WordMedian.java

@@ -0,0 +1,208 @@
+package org.apache.hadoop.examples;
+
+/**
+ * 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.
+ */
+
+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.IntWritable;
+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.TaskCounter;
+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;
+
+public class WordMedian extends Configured implements Tool {
+
+  private double median = 0;
+  private final static IntWritable ONE = new IntWritable(1);
+
+  /**
+   * Maps words from line of text into a key-value pair; the length of the word
+   * as the key, and 1 as the value.
+   */
+  public static class WordMedianMapper extends
+      Mapper<Object, Text, IntWritable, IntWritable> {
+
+    private IntWritable length = new IntWritable();
+
+    /**
+     * Emits a key-value pair for counting the word. Outputs are (IntWritable,
+     * IntWritable).
+     * 
+     * @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();
+        length.set(string.length());
+        context.write(length, ONE);
+      }
+    }
+  }
+
+  /**
+   * Performs integer summation of all the values for each key.
+   */
+  public static class WordMedianReducer extends
+      Reducer<IntWritable, IntWritable, IntWritable, IntWritable> {
+
+    private IntWritable val = new IntWritable();
+
+    /**
+     * Sums all the individual values within the iterator and writes them to the
+     * same key.
+     * 
+     * @param key
+     *          This will be a length of a word that was read.
+     * @param values
+     *          This will be an iterator of all the values associated with that
+     *          key.
+     */
+    public void reduce(IntWritable key, Iterable<IntWritable> values,
+        Context context) throws IOException, InterruptedException {
+
+      int sum = 0;
+      for (IntWritable value : values) {
+        sum += value.get();
+      }
+      val.set(sum);
+      context.write(key, val);
+    }
+  }
+
+  /**
+   * This is a standard program to read and find a median value based on a file
+   * of word counts such as: 1 456, 2 132, 3 56... Where the first values are
+   * the word lengths and the following values are the number of times that
+   * words of that length appear.
+   * 
+   * @param path
+   *          The path to read the HDFS file from (part-r-00000...00001...etc).
+   * @param medianIndex1
+   *          The first length value to look for.
+   * @param medianIndex2
+   *          The second length value to look for (will be the same as the first
+   *          if there are an even number of words total).
+   * @throws IOException
+   *           If file cannot be found, we throw an exception.
+   * */
+  private double readAndFindMedian(String path, int medianIndex1,
+      int medianIndex2, 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!");
+
+    BufferedReader br = null;
+
+    try {
+      br = new BufferedReader(new InputStreamReader(fs.open(file)));
+      int num = 0;
+
+      String line;
+      while ((line = br.readLine()) != null) {
+        StringTokenizer st = new StringTokenizer(line);
+
+        // grab length
+        String currLen = st.nextToken();
+
+        // grab count
+        String lengthFreq = st.nextToken();
+
+        int prevNum = num;
+        num += Integer.parseInt(lengthFreq);
+
+        if (medianIndex2 >= prevNum && medianIndex1 <= num) {
+          System.out.println("The median is: " + currLen);
+          br.close();
+          return Double.parseDouble(currLen);
+        } else if (medianIndex2 >= prevNum && medianIndex1 < num) {
+          String nextCurrLen = st.nextToken();
+          double theMedian = (Integer.parseInt(currLen) + Integer
+              .parseInt(nextCurrLen)) / 2.0;
+          System.out.println("The median is: " + theMedian);
+          br.close();
+          return theMedian;
+        }
+      }
+    } finally {
+      br.close();
+    }
+    // error, no median found
+    return -1;
+  }
+
+  public static void main(String[] args) throws Exception {
+    ToolRunner.run(new Configuration(), new WordMedian(), args);
+  }
+
+  @Override
+  public int run(String[] args) throws Exception {
+    if (args.length != 2) {
+      System.err.println("Usage: wordmedian <in> <out>");
+      return 0;
+    }
+
+    setConf(new Configuration());
+    Configuration conf = getConf();
+
+    @SuppressWarnings("deprecation")
+    Job job = new Job(conf, "word median");
+    job.setJarByClass(WordMedian.class);
+    job.setMapperClass(WordMedianMapper.class);
+    job.setCombinerClass(WordMedianReducer.class);
+    job.setReducerClass(WordMedianReducer.class);
+    job.setOutputKeyClass(IntWritable.class);
+    job.setOutputValueClass(IntWritable.class);
+    FileInputFormat.addInputPath(job, new Path(args[0]));
+    FileOutputFormat.setOutputPath(job, new Path(args[1]));
+    boolean result = job.waitForCompletion(true);
+
+    // Wait for JOB 1 -- get middle value to check for Median
+
+    long totalWords = job.getCounters()
+        .getGroup(TaskCounter.class.getCanonicalName())
+        .findCounter("MAP_OUTPUT_RECORDS", "Map output records").getValue();
+    int medianIndex1 = (int) Math.ceil((totalWords / 2.0));
+    int medianIndex2 = (int) Math.floor((totalWords / 2.0));
+
+    median = readAndFindMedian(args[1], medianIndex1, medianIndex2, conf);
+
+    return (result ? 0 : 1);
+  }
+
+  public double getMedian() {
+    return median;
+  }
+}

hadoop-mapreduce-project/src/examples/org/apache/hadoop/examples/WordStandardDeviation.java

@@ -0,0 +1,210 @@
+package org.apache.hadoop.examples;
+
+/**
+ * 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.
+ */
+
+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;
+
+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)));
+      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 {
+      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();
+
+    @SuppressWarnings("deprecation")
+    Job job = new Job(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;
+  }
+}

hadoop-mapreduce-project/src/test/mapred/org/apache/hadoop/examples/TestWordStats.java

@@ -0,0 +1,272 @@
+package org.apache.hadoop.examples;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.StringTokenizer;
+import java.util.TreeMap;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FileStatus;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.util.ToolRunner;
+import org.junit.Before;
+import org.junit.Test;
+
+public class TestWordStats {
+
+  private final static String INPUT = "src/test/mapred/org/apache/hadoop/examples/pi/math";
+  private final static String MEAN_OUTPUT = "build/data/mean_output";
+  private final static String MEDIAN_OUTPUT = "build/data/median_output";
+  private final static String STDDEV_OUTPUT = "build/data/stddev_output";
+
+  /**
+   * Modified internal test class that is designed to read all the files in the
+   * input directory, and find the standard deviation between all of the word
+   * lengths.
+   */
+  public static class WordStdDevReader {
+    private long wordsRead = 0;
+    private long wordLengthsRead = 0;
+    private long wordLengthsReadSquared = 0;
+
+    public WordStdDevReader() {
+    }
+
+    public double read(String path) throws IOException {
+      FileSystem fs = FileSystem.get(new Configuration());
+      FileStatus[] files = fs.listStatus(new Path(path));
+
+      for (FileStatus fileStat : files) {
+        if (!fileStat.isFile())
+          continue;
+
+        BufferedReader br = null;
+
+        try {
+          br = new BufferedReader(new InputStreamReader(fs.open(fileStat.getPath())));
+
+          String line;
+          while ((line = br.readLine()) != null) {
+            StringTokenizer st = new StringTokenizer(line);
+            String word;
+            while (st.hasMoreTokens()) {
+              word = st.nextToken();
+              this.wordsRead++;
+              this.wordLengthsRead += word.length();
+              this.wordLengthsReadSquared += (long) Math.pow(word.length(), 2.0);
+            }
+          }
+
+        } catch (IOException e) {
+          System.out.println("Output could not be read!");
+          throw e;
+        } finally {
+          br.close();
+        }
+      }
+
+      double mean = (((double) this.wordLengthsRead) / ((double) this.wordsRead));
+      mean = Math.pow(mean, 2.0);
+      double term = (((double) this.wordLengthsReadSquared / ((double) this.wordsRead)));
+      double stddev = Math.sqrt((term - mean));
+      return stddev;
+    }
+
+  }
+
+  /**
+   * Modified internal test class that is designed to read all the files in the
+   * input directory, and find the median length of all the words.
+   */
+  public static class WordMedianReader {
+    private long wordsRead = 0;
+    private TreeMap<Integer, Integer> map = new TreeMap<Integer, Integer>();
+
+    public WordMedianReader() {
+    }
+
+    public double read(String path) throws IOException {
+      FileSystem fs = FileSystem.get(new Configuration());
+      FileStatus[] files = fs.listStatus(new Path(path));
+
+      int num = 0;
+
+      for (FileStatus fileStat : files) {
+        if (!fileStat.isFile())
+          continue;
+
+        BufferedReader br = null;
+
+        try {
+          br = new BufferedReader(new InputStreamReader(fs.open(fileStat.getPath())));
+
+          String line;
+          while ((line = br.readLine()) != null) {
+            StringTokenizer st = new StringTokenizer(line);
+            String word;
+            while (st.hasMoreTokens()) {
+              word = st.nextToken();
+              this.wordsRead++;
+              if (this.map.get(word.length()) == null) {
+                this.map.put(word.length(), 1);
+              } else {
+                int count = this.map.get(word.length());
+                this.map.put(word.length(), count + 1);
+              }
+            }
+          }
+        } catch (IOException e) {
+          System.out.println("Output could not be read!");
+          throw e;
+        } finally {
+          br.close();
+        }
+      }
+
+      int medianIndex1 = (int) Math.ceil((this.wordsRead / 2.0));
+      int medianIndex2 = (int) Math.floor((this.wordsRead / 2.0));
+
+      for (Integer key : this.map.navigableKeySet()) {
+        int prevNum = num;
+        num += this.map.get(key);
+
+        if (medianIndex2 >= prevNum && medianIndex1 <= num) {
+          return key;
+        } else if (medianIndex2 >= prevNum && medianIndex1 < num) {
+          Integer nextCurrLen = this.map.navigableKeySet().iterator().next();
+          double median = (key + nextCurrLen) / 2.0;
+          return median;
+        }
+      }
+      return -1;
+    }
+
+  }
+
+  /**
+   * Modified internal test class that is designed to read all the files in the
+   * input directory, and find the mean length of all the words.
+   */
+  public static class WordMeanReader {
+    private long wordsRead = 0;
+    private long wordLengthsRead = 0;
+
+    public WordMeanReader() {
+    }
+
+    public double read(String path) throws IOException {
+      FileSystem fs = FileSystem.get(new Configuration());
+      FileStatus[] files = fs.listStatus(new Path(path));
+
+      for (FileStatus fileStat : files) {
+        if (!fileStat.isFile())
+          continue;
+
+        BufferedReader br = null;
+
+        try {
+          br = new BufferedReader(new InputStreamReader(fs.open(fileStat.getPath())));
+
+          String line;
+          while ((line = br.readLine()) != null) {
+            StringTokenizer st = new StringTokenizer(line);
+            String word;
+            while (st.hasMoreTokens()) {
+              word = st.nextToken();
+              this.wordsRead++;
+              this.wordLengthsRead += word.length();
+            }
+          }
+        } catch (IOException e) {
+          System.out.println("Output could not be read!");
+          throw e;
+        } finally {
+          br.close();
+        }
+      }
+
+      double mean = (((double) this.wordLengthsRead) / ((double) this.wordsRead));
+      return mean;
+    }
+
+  }
+
+  /**
+   * Internal class designed to delete the output directory. Meant solely for
+   * use before and after the test is run; this is so next iterations of the
+   * test do not encounter a "file already exists" error.
+   * 
+   * @param dir
+   *          The directory to delete.
+   * @return Returns whether the deletion was successful or not.
+   */
+  public static boolean deleteDir(File dir) {
+    if (dir.isDirectory()) {
+      String[] children = dir.list();
+      for (int i = 0; i < children.length; i++) {
+        boolean success = deleteDir(new File(dir, children[i]));
+        if (!success) {
+          System.out.println("Could not delete directory after test!");
+          return false;
+        }
+      }
+    }
+
+    // The directory is now empty so delete it
+    return dir.delete();
+  }
+
+  @Before public void setup() throws Exception {
+    deleteDir(new File(MEAN_OUTPUT));
+    deleteDir(new File(MEDIAN_OUTPUT));
+    deleteDir(new File(STDDEV_OUTPUT));
+  }
+
+  @Test public void testGetTheMean() throws Exception {
+    String args[] = new String[2];
+    args[0] = INPUT;
+    args[1] = MEAN_OUTPUT;
+
+    WordMean wm = new WordMean();
+    ToolRunner.run(new Configuration(), wm, args);
+    double mean = wm.getMean();
+
+    // outputs MUST match
+    WordMeanReader wr = new WordMeanReader();
+    assertEquals(mean, wr.read(INPUT), 0.0);
+  }
+
+  @Test public void testGetTheMedian() throws Exception {
+    String args[] = new String[2];
+    args[0] = INPUT;
+    args[1] = MEDIAN_OUTPUT;
+
+    WordMedian wm = new WordMedian();
+    ToolRunner.run(new Configuration(), wm, args);
+    double median = wm.getMedian();
+
+    // outputs MUST match
+    WordMedianReader wr = new WordMedianReader();
+    assertEquals(median, wr.read(INPUT), 0.0);
+  }
+
+  @Test public void testGetTheStandardDeviation() throws Exception {
+    String args[] = new String[2];
+    args[0] = INPUT;
+    args[1] = STDDEV_OUTPUT;
+
+    WordStandardDeviation wsd = new WordStandardDeviation();
+    ToolRunner.run(new Configuration(), wsd, args);
+    double stddev = wsd.getStandardDeviation();
+
+    // outputs MUST match
+    WordStdDevReader wr = new WordStdDevReader();
+    assertEquals(stddev, wr.read(INPUT), 0.0);
+  }
+
+}