我已经编写了一个mapreduce程序来解析csv中的值。
数据集如下-
普拉文，40020，婴儿，026A22015年4月12日
普拉文，40020，玩具，0383，1/04/2014
praveen，272，图书，033832013年3月14日
普拉文，22636，自行车，737，2012年12月24日
我的Map函数是从csv读取第一个值（即用户名）作为键，最后一个值（即日期）作为值
我的reduce函数也非常简单，我必须从特定键ie username的值列表中选择最新日期作为值
守则如下—

package com.test.mapreduce;
  import java.io.IOException;
  import java.text.ParseException;
  import java.text.SimpleDateFormat;
  import java.util.ArrayList;
  import java.util.Date;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Set;

  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.conf.Configured;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.io.IntWritable;
  import org.apache.hadoop.io.LongWritable;
  import org.apache.hadoop.io.Text;
  import org.apache.hadoop.mapred.FileInputFormat;
  import org.apache.hadoop.mapred.FileOutputFormat;
  import org.apache.hadoop.mapred.JobClient;
  import org.apache.hadoop.mapred.JobConf;
  import org.apache.hadoop.mapred.KeyValueTextInputFormat;
  import org.apache.hadoop.mapred.MapReduceBase;
  import org.apache.hadoop.mapred.Mapper;
  import org.apache.hadoop.mapred.OutputCollector;
  import org.apache.hadoop.mapred.Reducer;
  import org.apache.hadoop.mapred.Reporter;
  import org.apache.hadoop.mapred.TextInputFormat;
  import org.apache.hadoop.mapred.TextOutputFormat;
  import org.apache.hadoop.util.Tool;
  import org.apache.hadoop.util.ToolRunner;

 public class RetailCustomerAnalysis_2 extends Configured implements Tool {
             public static class MapClass extends MapReduceBase
             implements Mapper<LongWritable, Text, Text, Text> {

      private Text key1 = new Text();
      private Text value1 = new Text();
      private int noofFields = 5;

 public void map(LongWritable key, Text value,
                 OutputCollector<Text, Text> output,
                 Reporter reporter) throws IOException {

        String line = value.toString().replaceAll("\\s+","");
        String[] split = line.split(",");

        if(split.length!=noofFields){
        return;
        }

        else {
            key1.set(split[0].toString().trim()); 
            value1.set(split[4].toString().trim());
            System.out.println(split[4].toString().trim());
            output.collect(key1, value1);
     }
    }
  }

 public static class Reduce extends MapReduceBase
 implements Reducer<Text, Text, Text, Text> {

 public void reduce(Text key, Iterator<Text> values,
                    OutputCollector<Text, Text> output,
                    Reporter reporter) throws IOException {

     SimpleDateFormat formatter = new SimpleDateFormat("MM/dd/yyyy");
     Date date = new Date();

     List<Text> dateList = new ArrayList<Text>();

     for(Iterator<Text> it = values; it.hasNext();) {
         // add the values in the arrayList
         dateList.add((Text) it.next());
     }

     if(dateList.size()==1){ //If the mapper output has only one date , then select that date 
                             // as the VALUE
     try  {
            date = formatter.parse(dateList.get(0).toString());
          } catch (ParseException e) {
            e.printStackTrace();
        }
     } //If part ends 

     else {
             try {
               date = formatter.parse(dateList.get(0).toString()); 
                      //select the first date from list
             } catch (ParseException e1) {
               e1.printStackTrace();
             }

             for(int i=0 ; i <dateList.size();++i){
                   try {
                   //compare the selected date with the rest of the dates in the list.
                   if((formatter.parse(dateList.get(i).toString())).compareTo(date)>0){
                       date=formatter.parse(dateList.get(i).toString());
                       // getting the max date from the list
                        }
                   }
                   catch (ParseException e) {
                  e.printStackTrace();
                }
             } //for loops ends
     }  // else part ends    

     Text value = new Text(date.toString());
       output.collect(key, value);
      }
  }

 public int run(String[] args) throws Exception {
 Configuration conf = getConf();

 JobConf job = new JobConf(conf, RetailCustomerAnalysis_2.class);

 Path in = new Path(args[0]);
 Path out = new Path(args[1]);
 FileInputFormat.setInputPaths(job, in);
 FileOutputFormat.setOutputPath(job, out);

 job.setJobName("RetailCustomerAnalysis_2");
 job.setMapperClass(MapClass.class);
 job.setReducerClass(Reduce.class);

 job.setInputFormat(TextInputFormat.class);
 job.setOutputFormat(TextOutputFormat.class);
 job.setOutputKeyClass(Text.class);
 job.setOutputValueClass(Text.class);
 job.set("key.value.separator.in.input.line", ",");

 JobClient.runJob(job);
 return 0;
  }

public static void main(String[] args) throws Exception { 
 int res = ToolRunner.run(new Configuration(), new RetailCustomerAnalysis_2(), args);

 System.exit(res);
 }

 }

但我从名单上随机得到了一个日期。有人能帮忙吗。