Question

我正在Hadoop上实现一个PageRank算法，正如标题所示，我在尝试执行代码时想出了以下错误：

键入地图中的键不匹配：期望org.apache.hadoop.io.Text，收到org.apache.hadoop.io.LongWritable

在我的输入文件中，我将图形节点ID作为键存储，并将它们的一些信息存储为值。我的输入文件格式如下：

1 \ t 3.4,2,5,6,67

4 \ t 4.2,77,2,7,83

... ...

尝试理解错误说明我尝试使用LongWritable作为我的主变量类型，如下面的代码所示。这意味着我有：

地图＆LT; LongWritable，LongWritable，LongWritable，LongWritable＆gt;

减少＆LT; LongWritable，LongWritable，LongWritable，LongWritable＆gt;

但是，我也试过了：

地图＆LT;文字，文字，文字，文字＆gt;

减少＆LT;文字，文字，文字，文字＆gt;

还有：

地图＆LT; LongWritable，Text，LongWritable，Text＆gt;

减少＆LT; LongWritable，Text，LongWritable，Text＆gt;

我总是想出同样的错误。我想我无法理解错误中的预期和接收方式。这是否意味着我的地图函数从我的输入文件中预期LongWritable并且它有文本？我使用的输入文件的格式或变量类型是否有问题？

以下是完整的代码，您能告诉我要改变什么以及在哪里？：

import java.io.IOException;
import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.lang.Object.*;

import org.apache.commons.cli.ParseException;
import org.apache.commons.lang.StringUtils;
import org.apache.commons.configuration.Configuration;
import org.apache.hadoop.security.Credentials;
import org.apache.log4j.*;
import org.apache.commons.logging.*;
import org.apache.hadoop.mapred.*;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.JobContext;
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.SequenceFileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.SequenceFileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;



public class Pagerank
{   


public static class PRMap extends Mapper<LongWritable, LongWritable, LongWritable, LongWritable>
{

    public void map(LongWritable lineNum, LongWritable line, OutputCollector<LongWritable, LongWritable> outputCollector, Reporter reporter) throws IOException, InterruptedException
    {
        if (line.toString().length() == 0) {
            return;
        }

        Text key = new Text();
        Text value = new Text();
        LongWritable valuel = new LongWritable();
        StringTokenizer spline = new StringTokenizer(line.toString(),"\t");
        key.set(spline.nextToken());  
        value.set(spline.nextToken());  

        valuel.set(Long.parseLong(value.toString()));
        outputCollector.collect(lineNum,valuel);


        String info = value.toString();
        String splitter[] = info.split(",");

        if(splitter.length >= 3)
        {
            float f = Float.parseFloat(splitter[0]);
            float pagerank = f / (splitter.length - 2);

            for(int i=2;i<splitter.length;i++)
            {
                LongWritable key2 = new LongWritable();
                LongWritable value2 = new LongWritable();
                long l;

                l = Long.parseLong(splitter[i]);
                key2.set(l);
                //key2.set(splitter[i]);
                value2.set((long)f);

                outputCollector.collect(key2, value2);
            }
        }
    }
}

public static class PRReduce extends Reducer<LongWritable,LongWritable,LongWritable,LongWritable>
{
    private Text result = new Text();
    public void reduce(LongWritable key, Iterator<LongWritable> values,OutputCollector<LongWritable, LongWritable> results, Reporter reporter) throws IOException, InterruptedException
    {

        float pagerank = 0;
        String allinone = ",";
        while(values.hasNext())
        {
            LongWritable temp = values.next();
            String converted = temp.toString();
            String[] splitted = converted.split(",");

            if(splitted.length > 1)
            {                   
                for(int i=1;i<splitted.length;i++)
                {
                    allinone = allinone.concat(splitted[i]);
                    if(i != splitted.length - 1)
                        allinone = allinone.concat(",");
                }
            }
            else
            {
                float f = Float.parseFloat(splitted[0]);
                pagerank = pagerank + f;
            }
        }
        String last = Float.toString(pagerank);
        last = last.concat(allinone);

        LongWritable value = new LongWritable();
        value.set(Long.parseLong(last));

        results.collect(key, value);
    }      
}



public static void main(String[] args) throws Exception
{      


    org.apache.hadoop.conf.Configuration conf = new org.apache.hadoop.conf.Configuration();

    String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
    if (otherArgs.length != 2) {
      System.err.println("Usage: wordcount <in> <out>");
      System.exit(2);
    }

    Job job = new Job(conf, "pagerank_itr0");

    job.setJarByClass(Pagerank.class);      
    job.setMapperClass(Pagerank.PRMap.class);       
    job.setReducerClass(Pagerank.PRReduce.class);    


    job.setOutputKeyClass(LongWritable.class);            
    job.setOutputValueClass(LongWritable.class);            
    FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
    FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
    job.waitForCompletion(true);

}
}

Answer 1

您没有在作业配置中设置Mapper输出类。尝试使用以下方法设置Job中的键和值类：

setMapOutputKeyClass（）;

setMapOutputValueClass（）;

执行中出现Hadoop错误：键入map中的键不匹配：expect org.apache.hadoop.io.Text，recieved org.apache.hadoop.io.LongWritable

1 个答案: