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September 21, 2011 03:17
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// G R Fischer for Fall 2011 Cloud Computing and Storage | |
// WordCount - Programming assignment 1, part 1 of 3 | |
// 2011-09-20 | |
// Derived from many different example WordCount programs. | |
package org.myorg; | |
import java.io.IOException; | |
import java.util.*; | |
import java.util.regex.*; | |
import org.apache.hadoop.fs.Path; | |
import org.apache.hadoop.conf.*; | |
import org.apache.hadoop.io.*; | |
import org.apache.hadoop.mapred.*; | |
import org.apache.hadoop.util.*; | |
public class WordCount { | |
// The map task breaks a text up into individual words, emitting the intermediate | |
// key, value pairs: | |
// | |
// word, 1 | |
// | |
// Some cleanup is done over the emitted words: they are lower-cased and odd characters | |
// are removed. Trailing or leading apostrophes are particularly troublesome with | |
// Shakespearean texts. | |
public static class Map extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> { | |
private final static IntWritable one = new IntWritable(1); | |
private Text word = new Text(); | |
// cleanup regexp to try to get Shakespeare's spelling consistent: but leaves internal apostrophes, dashes | |
private Pattern pattern = Pattern.compile("^[^0-9a-z]+|[^0-9a-z]+$|[^0-9a-z'-]"); | |
private Matcher matcher = pattern.matcher(""); // we'll reset as we use | |
public void map(LongWritable key, Text value, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException { | |
String line = value.toString(); | |
StringTokenizer tokenizer = new StringTokenizer(line); | |
while (tokenizer.hasMoreTokens()) { | |
matcher.reset(tokenizer.nextToken().toLowerCase()); | |
word.set(matcher.replaceAll("")); | |
output.collect(word, one); | |
} | |
} | |
} | |
// Reduce, given input as single word with a list of occurences, e.g. | |
// | |
// foo, (1, 1, 2) | |
// | |
// folds to summed occurrences | |
// | |
// foo, 4 | |
// | |
// Because we use this class as a combiner as well as a reducer, the reduction phase | |
// may get occurences > 1 | |
public static class Reduce extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> { | |
public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException { | |
int sum = 0; | |
while (values.hasNext()) { | |
sum += values.next().get(); | |
} | |
output.collect(key, new IntWritable(sum)); | |
} | |
} | |
// Boiler plate setup | |
public static void main(String[] args) throws Exception { | |
JobConf conf = new JobConf(WordCount.class); | |
conf.setJobName("wordcount"); | |
// don't compress the output (was default on EC2 hadoop instance I used) | |
conf.setBoolean("mapred.output.compress", false); | |
// hardcoded instances; no particular reason for these numbers | |
conf.setNumMapTasks(3); | |
conf.setNumReduceTasks(2); | |
// Setup intermediate key/value domain | |
conf.setOutputKeyClass(Text.class); | |
conf.setOutputValueClass(IntWritable.class); | |
// Note, use reducer as combiner | |
conf.setMapperClass(Map.class); | |
conf.setCombinerClass(Reduce.class); | |
conf.setReducerClass(Reduce.class); | |
// input/output plain text | |
conf.setInputFormat(TextInputFormat.class); | |
conf.setOutputFormat(TextOutputFormat.class); | |
// input/output directories | |
FileInputFormat.setInputPaths(conf, new Path(args[0])); | |
FileOutputFormat.setOutputPath(conf, new Path(args[1])); | |
JobClient.runJob(conf); | |
} | |
} |
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