首先，我是java的初学者，但我必须尽快完成MapReduce Job的任务。
我试图修改wordcount算法，因为问题非常相似。
我的输入是一个文本文件，其中包含一列数据：
double**MapReduce作业必须设置每行的第一个字符串，如我的键（日期：2008-10-23Hour：03User：001）和数字1或0，如值。 reducer的任务只是对同一个键的值（1 + 1 + 0 + 1 + 0 ...）求和......这就是全部。 问题是，在结果中，我得到的数字（太大）像最终值一样，但我不能完全知道原因。
这是算法：
Date:2008-10-23Hour:02User:000 1
Date:2008-10-23Hour:02User:000 0
Date:2008-10-23Hour:02User:000 1
Date:2008-10-23Hour:02User:000 1
Date:2008-10-23Hour:02User:000 0
Date:2008-10-23Hour:02User:000 1
Date:2008-10-23Hour:02User:000 1
Date:2008-10-23Hour:02User:000 0
Date:2008-10-23Hour:02User:000 1
Date:2008-10-23Hour:02User:000 1
Date:2008-10-23Hour:02User:000 1
Date:2008-10-23Hour:03User:000 0
Date:2008-10-23Hour:03User:000 1
Date:2008-10-23Hour:03User:000 1
Date:2008-10-23Hour:03User:000 0
Date:2008-10-23Hour:03User:000 1
Date:2008-10-23Hour:03User:000 1
Date:2008-10-23Hour:03User:000 0
Date:2008-10-23Hour:04User:000 1
Date:2008-10-23Hour:04User:000 0
Date:2008-10-23Hour:04User:000 1
Date:2008-10-23Hour:04User:000 1
Date:2008-10-23Hour:04User:000 1
Date:2008-10-23Hour:04User:000 1
Date:2008-10-23Hour:04User:000 0
Date:2008-10-23Hour:04User:000 1
Date:2008-10-23Hour:04User:000 0
Date:2008-10-23Hour:04User:000 1
这些都是错误的输出：
日期：2008-10-23hour：02User：000 16
日期：2008-10-23Hour：03User：000 6
日期：2008-10-23hour：04User：000 14
正确的输出应该是：
日期：2008-10-23hour：02User：000 8
日期：2008-10-23Hour：03User：000 3
日期：2008-10-23Hour：04User：000 7
错误的结果恰好是正确结果的两倍
此外，如果我在计算过程中使用值（0或1）打印总和和键，我会得到：
import java.io.BufferedReader;
import java.io.FileReader;
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.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.Reducer.Context;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
public class MapReduce {
public static class KeyValueMapper
extends Mapper<Object, Object , Text, IntWritable>{
private IntWritable ValueDistanceFunction = new IntWritable();
private Text DateHourUser = new Text();
public void map(Object key, Object value, Context context
) throws IOException, InterruptedException {
StringTokenizer itr = new StringTokenizer(value.toString());
while (itr.hasMoreTokens()) {
DateHourUser.set(read.nextToken());
ValueDistanceFunction.set(Integer.parseInt(read.nextToken()));
context.write(DateHourUser,ValueDistanceFunction);
// I print the results only to check them
System.out.println(DateHourUser);
System.out.println(ValueDistanceFunction);
}
}
}
public static class IntSumReducer
extends Reducer<Text,IntWritable,Text,IntWritable> {
private IntWritable result = new IntWritable();
public void reduce(Text key, Iterable<IntWritable>values,
Context context
) throws IOException, InterruptedException {
int sum =0;
for (IntWritable val : values) {
sum += val.get();
System.out.println(sum);
}
result.set(sum);
context.write(key,result);
}
}
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf, "KeyValue");
job.setJarByClass(MapReduce.class);
job.setMapperClass(KeyValueMapper.class);
job.setCombinerClass(IntSumReducer.class);
job.setReducerClass(IntSumReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
FileInputFormat.addInputPath(job, new Path("/home/ubuntu/workspace/FileGeneration/Input"));
FileOutputFormat.setOutputPath(job, new Path("/home/ubuntu/workspace/FileGeneration/Output"));
System.exit(job.waitForCompletion(true) ? 0:1);
}
}
提前多多感谢。
答案 0 :(得分：1)
问题在于您的Mapper代码。你为什么要在映射器中读取输入？
以下行有问题：
BufferedReader sc=new BufferedReader(new FileReader("/home/ubuntu/workspace/FileGeneration/Input/Input"));
String line;
while ((line=sc.readLine()) !=null){
StringTokenizer read= new StringTokenizer (line," ");
while (read.hasMoreTokens()){
您已在Driver类中指定了输入。
FileInputFormat.addInputPath(job, new Path("/home/ubuntu/workspace/FileGeneration/Input"));
在Mapper中无需再次读取此输入。 Framework读取此文件并将每行传递给Mapper。该行包含在value。
您的Mapper代码应如下所示：
public void map(Object key, Object value, Context context
) throws IOException, InterruptedException {
StringTokenizer itr = new StringTokenizer(value.toString());
while (itr.hasMoreTokens()) {
DateHourUser.set(read.nextToken());
ValueDistanceFunction.set(Integer.parseInt(read.nextToken()));
context.write(DateHourUser,ValueDistanceFunction);
// I print the results only to check them
System.out.println(DateHourUser);
System.out.println(ValueDistanceFunction);
}
}
修改 我拿走了你的数据并运行了程序。我得到了以下结果。我发现数据或代码没有问题：
E:\hdp\hadoop-2.7.1.2.3.0.0-2557\bin>hadoop fs -cat /user/mballur/Output/part-r-00000
Date:2008-10-23Hour:02User:000 8
Date:2008-10-23Hour:03User:000 4
Date:2008-10-23Hour:04User:000 7
该计划没有问题。