Hadoop实战-MapReduce之分组(group-by)统计(七)

1、数据准备

使用MapReduce计算age.txt中年龄最大、最小、均值
name,min,max,count
Mike,35,20,1
Mike,5,15,2
Mike,20,13,1
Steven,40,20,10
Ken,28,68,1
Ken,14,198,10
Cindy,32,31,100

2、预期结果
Mike 5 20 4
Steven,40,20,10
Ken   14 198 11
Cindy,32,31,100

3、需要加入自定义输出类型MinMaxCountTuple

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import org.apache.hadoop.io.Writable;

public class MinMaxCountTuple implements Writable {
	private int min;
	private int max;
	private int count;

	public int getMin() {
		return min;
	}

	public void setMin(int min) {
		this.min = min;
	}

	public int getMax() {
		return max;
	}

	public void setMax(int max) {
		this.max = max;
	}

	public int getCount() {
		return count;
	}

	public void setCount(int count) {
		this.count = count;
	}

	public void readFields(DataInput in) throws IOException {
		min = in.readInt();
		max = in.readInt();
		count = in.readInt();
	}

	public void write(DataOutput out) throws IOException {
		out.writeInt(min);
		out.writeInt(max);
		out.writeInt(count);
	}

	@Override
	public String toString() {
		return min + "\t" + max + "\t" + count;
	}
}

4、MapReduce编程

import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
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.GenericOptionsParser;

public class Age {
	public static class AgeMap extends
			Mapper<Object, Text, Text, MinMaxCountTuple> {

		private Text userName = new Text();
		private MinMaxCountTuple outTuple = new MinMaxCountTuple();

		@Override
		public void map(Object key, Text value, Context context)
				throws IOException, InterruptedException {
			StringTokenizer itr = new StringTokenizer(value.toString());
			while (itr.hasMoreTokens()) {
				String content = itr.nextToken();
				String[] splits = content.split(",");
				String name = splits[0];
				int min = Integer.valueOf(splits[1]);
				int max = Integer.valueOf(splits[2]);
				int count = Integer.valueOf(splits[3]);
				outTuple.setMin(min);
				outTuple.setMax(max);
				outTuple.setCount(count);
				userName.set(name);
				context.write(userName, outTuple);
			}
		}
	}

	public static class AgeReduce extends
			Reducer<Text, MinMaxCountTuple, Text, MinMaxCountTuple> {
		private MinMaxCountTuple result = new MinMaxCountTuple();

		public void reduce(Text key, Iterable<MinMaxCountTuple> values,
				Context context) throws IOException, InterruptedException {
			int sum = 0;
			result.setMax(0);
			result.setMin(Integer.MAX_VALUE);
			for (MinMaxCountTuple tmp : values) {
				if (tmp.getMin() < result.getMin()) {
					result.setMin(tmp.getMin());
				}
				if (tmp.getMax() > result.getMax()) {
					result.setMax(tmp.getMax());
				}
				sum += tmp.getCount();
			}
			result.setCount(sum);
			context.write(key, result);
		}
	}

	public static void main(String[] args) throws Exception {
		Configuration conf = new Configuration();
		String[] otherArgs = new GenericOptionsParser(conf, args)
				.getRemainingArgs();
		if (otherArgs.length != 2) {
			System.err.println("Usage: MinMaxCountDriver <in> <out>");
			System.exit(2);
		}
		Job job = new Job(conf, "StackOverflow Comment Date Min Max Count");
		job.setJarByClass(Age.class);
		job.setMapperClass(AgeMap.class);
		job.setCombinerClass(AgeReduce.class);
		job.setReducerClass(AgeReduce.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(MinMaxCountTuple.class);
		FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
		FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}
}