Question

我在使用MapReduce作业时遇到问题。我的map函数运行并产生所需的输出。但是，reduce函数不会运行。似乎函数永远不会被调用。我使用Text作为键，Text作为值。但我不认为这会导致问题。

输入文件的格式如下：

2015-06-06,2015-06-06,40.80239868164062,-73.93379211425781,40.72591781616211,-73.98358154296875,7.71,35.72
2015-06-06,2015-06-06,40.71020126342773,-73.96302032470703,40.72967529296875,-74.00226593017578,3.11,2.19
2015-06-05,2015-06-05,40.68404388427734,-73.97597503662109,40.67932510375977,-73.95581817626953,1.13,1.29
...

我想将行的第二个日期提取为Text，并将其用作reduce的键。密钥的值将是同一行中最后两个float值的组合即：2015-06-06 7.71 35.72 2015-06-06 9.71 66.72
这样可以将值部分视为由空格分隔的两列这实际上是有效的，我得到一个输出文件具有许多相同的键但不同的值。

现在我想总结每个键的两个浮点列，以便在reduce之后我得到一个日期作为键，并将总计列作为值。

问题：减少不运行。

请参阅以下代码：

映射

public class Aggregate {

public static class EarnDistMapper extends Mapper<Object, Text, Text, Text> {

    public void map(Object key, Text value, Context context) throws IOException, InterruptedException {

        String [] splitResult = value.toString().split(",");
        String dropOffDate = "";
        String compEarningDist = "";
        //dropoffDate at pos 1 as key 
        dropOffDate = splitResult[1];
        //distance at pos length-2 and earnings at pos length-1 as values separated by space
        compEarningDist = splitResult[splitResult.length -2] + " " + splitResult[splitResult.length-1];

        context.write(new Text(dropOffDate), new Text(compEarningDist));
    }
}

减速

public static class EarnDistReducer extends Reducer<Text,Text,Text,Text> {

    public void reduce(Text key, Iterator<Text> values, Context context) throws IOException, InterruptedException {

         float sumDistance = 0;
         float sumEarnings = 0;
         String[] splitArray; 

         while (values.hasNext()){
             splitArray = values.next().toString().split("\\s+");
             //distance first
             sumDistance += Float.parseFloat(splitArray[0]);
             sumEarnings += Float.parseFloat(splitArray[1]);
         }

         //combine result to text

         context.write(key, new Text(Float.toString(sumDistance) + " " + Float.toString(sumEarnings)));
    }
}

作业

public static void main(String[] args) throws Exception{
    // TODO
    Configuration conf = new Configuration();

    Job job = Job.getInstance(conf, "Taxi dropoff");
    job.setJarByClass(Aggregate.class);
    job.setMapperClass(EarnDistMapper.class);
    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(Text.class);
    job.setCombinerClass(EarnDistReducer.class);
    job.setReducerClass(EarnDistReducer.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(Text.class);

    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}

感谢您的帮助!!

Answer 1

您有reduce方法的签名错误。你有：

public void reduce(Text key, Iterator<Text> values, Context context) {

应该是：

public void reduce(Text key, Iterable<Text> values, Context context) {

Hadoop Reducer不起作用

1 个答案: