FriendsMapper.java Source code

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Here is the source code for FriendsMapper.java

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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 com.hadoop.examples.anagrams;

import java.io.IOException;
import java.util.Arrays;
import java.util.*;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.MapReduceBase;
import org.apache.hadoop.mapred.Mapper;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reporter;

/**
 * The Anagram mapper class gets a word as a line from the HDFS input and sorts the
 * letters in the word and writes its back to the output collector as 
 * Key : sorted word (letters in the word sorted)
 * Value: the word itself as the value.
 * When the reducer runs then we can group anagrams togather based on the sorted key.
 * 
 * @author subbu iyer
 *
 */
public class FriendsMapper extends MapReduceBase implements Mapper<LongWritable, Text, Text, Text> {

    private Text sortedText = new Text();
    private Text orginalText = new Text();

    public void map(LongWritable key, Text value, OutputCollector<Text, Text> outputCollector, Reporter reporter)
            throws IOException {

        // value => A:B,C,D,E

        String[] kv = value.toString().split(":");
        // kv[0] = A / kv[1] = B,C,D,E
        String k = kv[0];
        // k = A;

        List<String> vs = Arrays.asList(kv[1].split(","));
        // vs = {B,C,D,E}

        String values = kv[1];

        orginalText.set(values);

        for (String v : vs) { // v = {B,C,D,E}

            List<String> ks = new ArrayList<String>();
            // ks = {}
            ks.add(k);
            // ks = {A}
            ks.add(v);
            // ks = {A,v}
            Collections.sort(ks);

            sortedText.set(String.join(",", ks));
            // A,v
            outputCollector.collect(sortedText, orginalText);
        }

    }

}