Analysis.A2_Top_20_Most_Popular_Artists.Top_20_Most_Popular_Artist_Reducer.java Source code

Introduction

Here is the source code for Analysis.A2_Top_20_Most_Popular_Artists.Top_20_Most_Popular_Artist_Reducer.java

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package Analysis.A2_Top_20_Most_Popular_Artists;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

import java.io.IOException;
import java.util.Collections;
import java.util.Map;
import java.util.TreeMap;

/**
 *
 * @author Chintan
 */
public class Top_20_Most_Popular_Artist_Reducer extends Reducer<Text, IntWritable, NullWritable, Text> {
    private TreeMap<Integer, String> top20 = new TreeMap<Integer, String>(Collections.reverseOrder());

    public void reduce(Text key, Iterable<IntWritable> values, Context context)
            throws IOException, InterruptedException {
        int totalUniquePlayCount = 0;

        // get count and add
        for (IntWritable uniqueCount : values) {
            totalUniquePlayCount += uniqueCount.get();
        }

        //add this artist with its play count to tree map
        top20.put(totalUniquePlayCount, key.toString());

        // if map size has grown > 20 then remove first entry as tree map sorts in ascending order
        if (top20.size() > 20) {
            top20.remove(top20.lastKey());
        }
    }

    // Will be called once all keys are parsed
    @Override
    protected void cleanup(Context context) throws IOException, InterruptedException {
        for (Map.Entry<Integer, String> entry : top20.entrySet()) {

            //Integer key = entry.getKey();
            String value = entry.getValue().substring(0, 1).toUpperCase() + entry.getValue().substring(1);

            // print atop 20 artists
            context.write(NullWritable.get(), new Text(value));
        }
    }

}