china：张三 78李四 89王五 96赵六 67english张三 80李四 82王五    84赵六 86math张三 88李四 99王五 66赵六 77

import java.io.IOException;import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.FloatWritable;
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.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.reduce.IntSumReducer;public class MyAverage {public static class FormatMapper extends Mapper<Object, Text, Text, IntWritable>{private IntWritable val = new IntWritable();public void map(Object key, Text value, Context context) throws IOException, InterruptedException{String line[] = value.toString().split("\\s");val.set(Integer.parseInt(line[1]));context.write(new Text(line[0]), val);}}public static class AverageReducer extends Reducer<Text, IntWritable, Text, FloatWritable>{public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException{int count = 0;int sum = 0;for (IntWritable val : values) {sum += val.get();count ++;}float ave = (float)sum / count;context.write(key, new FloatWritable(ave));}}public static void main(String[] args) throws Exception {String dir_in = "hdfs://localhost:9000/in_average";String dir_out = "hdfs://localhost:9000/out_average";Path in = new Path(dir_in);Path out = new Path(dir_out);Configuration conf = new Configuration();Job averageJob = new Job(conf, "my_average");averageJob.setJarByClass(MyAverage.class);averageJob.setInputFormatClass(TextInputFormat.class);averageJob.setMapperClass(FormatMapper.class);averageJob.setCombinerClass(IntSumReducer.class);//countJob.setPartitionerClass(HashPartitioner.class);averageJob.setMapOutputKeyClass(Text.class);averageJob.setMapOutputValueClass(IntWritable.class);FileInputFormat.addInputPath(averageJob, in);averageJob.setReducerClass(AverageReducer.class);//averageJob.setNumReduceTasks(1);averageJob.setOutputKeyClass(Text.class);averageJob.setOutputValueClass(FloatWritable.class);//countJob.setOutputFormatClass(SequenceFileOutputFormat.class);
FileOutputFormat.setOutputPath(averageJob, out);averageJob.waitForCompletion(true);}}

张三    82.0
李四    90.0
王五    82.0
赵六    76.666664