Word Count (Map Reduce)

lintcode

Using map reduce to count word frequency.

https://hadoop.apache.org/docs/r1.2.1/mapred_tutorial.html#Example%3A+WordCount+v1.0

Example

chunk1: "Google Bye GoodBye Hadoop code"
chunk2: "lintcode code Bye"


Get MapReduce result:
    Bye: 2
    GoodBye: 1
    Google: 1
    Hadoop: 1
    code: 2
    lintcode: 1

思路

/**
 * Definition of OutputCollector:
 * class OutputCollector<K, V> {
 *     public void collect(K key, V value);
 *         // Adds a key/value pair to the output buffer
 * }
 */
public class WordCount {

    public static class Map {
        public void map(String key, String value, OutputCollector<String, Integer> output) {
            // Write your code here
            // Output the results into output buffer.
            // Ps. output.collect(String key, int value);
            String[] words = value.split("\\s");
            for (int i = 0; i < words.length; i++) {
                output.collect(words[i], 1);
            }
        }
    }

    public static class Reduce {
        public void reduce(String key, Iterator<Integer> values,
                           OutputCollector<String, Integer> output) {
            // Write your code here
            // Output the results into output buffer.
            // Ps. output.collect(String key, int value);
            int sum = 0;
            while (values.hasNext()) {
                sum += values.next();
            }

            output.collect(key, sum);
        }
    }
}