? 另外一个hadoop的入门demo，求平均数。是对wordcount这个demo的一个小小的修改。输入一堆成绩单（人名，成绩），然后求每个人成绩平均数，比如： //? subject1.txt ? a 90 ? b 80 ? c 70 ?// subject2.txt ? a 100 ? b 90 ? c 80 ? 求a,b,c这三个人的平均
? 另外一个hadoop的入门demo，求平均数。是对wordcount这个demo的一个小小的修改。输入一堆成绩单（人名，成绩），然后求每个人成绩平均数，比如：
//? subject1.txt
? a 90
? b 80
? c 70
?// subject2.txt
? a 100
? b 90
? c 80
? 求a,b,c这三个人的平均分。解决思路很简单，在map阶段key是名字，value是成绩，直接output。reduce阶段得到了map输出的key名字，values是该名字对应的一系列的成绩，那么对其求平均数即可。
? 这里我们实现了两个版本的代码，分别用textinputformat和 keyvaluetextinputformat来作为输入格式。
? textinputformat版本：
?
import java.util.*;
import java.io.*;
import org.apache.hadoop.conf.configuration;
import org.apache.hadoop.fs.path;
import org.apache.hadoop.io.text;
import org.apache.hadoop.io.intwritable;
import org.apache.hadoop.mapreduce.mapper;
import org.apache.hadoop.mapreduce.reducer;
import org.apache.hadoop.mapreduce.job;
import org.apache.hadoop.mapreduce.lib.input.fileinputformat;
import org.apache.hadoop.mapreduce.lib.output.fileoutputformat;
public class avescore {
public static class avemapper extends mapper
{
@override
public void map(object key, text value, context context) throws ioexception, interruptedexception
{
string line = value.tostring();
string[] strs = line.split(" ");
string name = strs[0];
int score = integer.parseint(strs[1]);
context.write(new text(name), new intwritable(score));
}
}
public static class avereducer extends reducer
{
@override
public void reduce(text key, iterable values, context context) throws ioexception, interruptedexception
{
int sum = 0;
int count = 0;
for(intwritable val : values)
{
sum += val.get();
count++;
}
int avescore = sum / count;
context.write(key, new intwritable(avescore));
}
}
public static void main(string[] args) throws exception
{
configuration conf = new configuration();
job job = new job(conf,"averagescore");
job.setjarbyclass(avescore.class);
job.setmapperclass(avemapper.class);
job.setreducerclass(avereducer.class);
job.setoutputkeyclass(text.class);
job.setoutputvalueclass(intwritable.class);
fileinputformat.addinputpath(job, new path(args[0]));
fileoutputformat.setoutputpath(job, new path(args[1]));
system.exit( job.waitforcompletion(true) ? 0 : 1);
}
}
keyvaluetextinputformat版本；
import java.util.*;
import java.io.*;
import org.apache.hadoop.conf.configuration;
import org.apache.hadoop.fs.path;
import org.apache.hadoop.io.text;
import org.apache.hadoop.io.intwritable;
import org.apache.hadoop.mapreduce.mapper;
import org.apache.hadoop.mapreduce.reducer;
import org.apache.hadoop.mapreduce.job;
import org.apache.hadoop.mapreduce.lib.input.fileinputformat;
import org.apache.hadoop.mapreduce.lib.output.fileoutputformat;
import org.apache.hadoop.mapreduce.lib.input.keyvaluetextinputformat;
import org.apache.hadoop.mapreduce.lib.output.textoutputformat;
public class avescore_keyvalue {
public static class avemapper extends mapper
{
@override
public void map(text key, text value, context context) throws ioexception, interruptedexception
{
int score = integer.parseint(value.tostring());
context.write(key, new intwritable(score) );
}
}
public static class avereducer extends reducer
{
@override
public void reduce(text key, iterable values, context context) throws ioexception, interruptedexception
{
int sum = 0;
int count = 0;
for(intwritable val : values)
{
sum += val.get();
count++;
}
int avescore = sum / count;
context.write(key, new intwritable(avescore));
}
}
public static void main(string[] args) throws exception
{
configuration conf = new configuration();
conf.set("mapreduce.input.keyvaluelinerecordreader.key.value.separator", " ");
job job = new job(conf,"averagescore");
job.setjarbyclass(avescore_keyvalue.class);
job.setmapperclass(avemapper.class);
job.setreducerclass(avereducer.class);
job.setoutputkeyclass(text.class);
job.setoutputvalueclass(intwritable.class);
job.setinputformatclass(keyvaluetextinputformat.class);
job.setoutputformatclass(textoutputformat.class) ;
fileinputformat.addinputpath(job, new path(args[0]));
fileoutputformat.setoutputpath(job, new path(args[1]));
system.exit( job.waitforcompletion(true) ? 0 : 1);
}
}
输出结果为：
? a 95
? b 85
? c 75
?
作者：qiul12345 发表于2013-8-23 21:51:03 原文链接
阅读：113 评论：0 查看评论
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