mapreduce编程：求平均值

package my.hadoopstudy;

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;

import java.io.IOException;

public class AvgCompute {

public static class MyMapper extends Mapper<Object, Text, Text, Text>{

public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
String[] e = value.toString().split(" ",2);
context.write(new Text(e[0]),new Text(e[1]));
}
}

public static class MyReducer extends Reducer<Text,Text,Text,Text> {

public void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
float sum = 0;
float count=0;
for (Text val : values) {
sum += Float.parseFloat(val.toString());
count +=1.0f;
}
sum=sum/count;
context.write(key,new Text(String.valueOf(sum)));
}
}

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: EventCount <in> <out>");
System.exit(2);
}
Job job = Job.getInstance(conf, "avg compute");
job.setJarByClass(AvgCompute.class);
job.setMapperClass(MyMapper.class);
job.setCombinerClass(MyReducer.class);
job.setReducerClass(MyReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}