MapReduce编程：平均成绩

问题描述

现在有三个文件分别代表学生的各科成绩，编程求各位同学的平均成绩。

                   

编程思想

map函数将姓名作为key，成绩作为value输出，reduce根据key即可将三门成绩相加。

代码

 package org.apache.hadoop.examples;
 
 import java.io.IOException;
 import java.util.Iterator;
 import java.util.StringTokenizer;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.io.IntWritable;
 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;
 
 public class calcGPA {
     public calcGPA() {
     }
 
     public static void main(String[] args) throws Exception {
         Configuration conf = new Configuration();
 
         String fileAddress = "hdfs://localhost:9000/user/hadoop/";
 
         //String[] otherArgs = (new GenericOptionsParser(conf, args)).getRemainingArgs();
         String[] otherArgs = new String[]{fileAddress+"score1.txt", fileAddress+"score2.txt", fileAddress+"score3.txt", fileAddress+"output"};
         if(otherArgs.length < 2) {
             System.err.println("Usage: calcGPA <in> [<in>...] <out>");
             System.exit(2);
         }
 
         Job job = Job.getInstance(conf, "calc GPA");
         job.setJarByClass(calcGPA.class);
         job.setMapperClass(calcGPA.TokenizerMapper.class);
         job.setCombinerClass(calcGPA.IntSumReducer.class);
         job.setReducerClass(calcGPA.IntSumReducer.class);
         job.setOutputKeyClass(Text.class);
         job.setOutputValueClass(IntWritable.class);
 
         for(int i = 0; i < otherArgs.length - 1; ++i) {
             FileInputFormat.addInputPath(job, new Path(otherArgs[i]));
         }
 
         FileOutputFormat.setOutputPath(job, new Path(otherArgs[otherArgs.length - 1]));
         System.exit(job.waitForCompletion(true)?0:1);
     }
 
     public static class IntSumReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
 
         public IntSumReducer() {
         }
 
         public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
             int sum = 0;
             int count = 0;
 
             IntWritable val;
             for(Iterator i$ = values.iterator(); i$.hasNext(); sum += val.get(),count++) {
                 val = (IntWritable)i$.next();
             }
 
             int average = (int)sum/count;
             context.write(key, new IntWritable(average));
         }
     }
 
     public static class TokenizerMapper extends Mapper<Object, Text, Text, IntWritable> {
 
         public TokenizerMapper() {
         }
 
         public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
             StringTokenizer itr = new StringTokenizer(value.toString(), "\n");
 
             while(itr.hasMoreTokens()) {
                 StringTokenizer iitr = new StringTokenizer(itr.nextToken());
                 String name = iitr.nextToken();
                 String score = iitr.nextToken();
                 context.write(new Text(name), new IntWritable(Integer.parseInt(score)));
             }
 
         }
     }
 }

疑问

在写这个的时候，我遇到个问题，就是输入输出文件的默认地址，为什么是user/hadoop/，我看了一下配置文件的信息，好像也没有出现过这个地址啊，希望有人能解答一下，万分感谢。