Mapreduce：平均计算不起作用

我正在尝试使用此 map reduce 代码来计算平均值，但由于某种原因，平均值计算不正确。这个想法是计算每年的平均电影评分

映射器代码

public class AverageRatingMapper extends Mapper<LongWritable, Text, Text, DoubleWritable>
{
    //initialize the writable datatype variables
    private final static DoubleWritable tempWritable = new DoubleWritable(0);
    private Text ReleaseYear = new Text();
    
    //Override the original map methods
    @Override
    //map takes in three parameters
    public void map(LongWritable key, Text value, Context context)
            throws IOException, InterruptedException
    {
        //creating an array called line of type String
        //Split the values in the fields and store each value in one array element
        String[] line = value.toString().split("\t");
        
        //create a variable ID with type String and store the the 4th element (index 3) from array line. This contains the Year in th data file
        String Year = line[3];
        
        //Set the value of the year object created from the Text class to be the value of the Year read from the data file
        ReleaseYear.set(Year);
        
        //Create a variable, temp, of type double and convert the value stored in the 15th element (14th index) of the line array from String to Double and store it in temp
        double temp = Double.parseDouble(line[14].trim());
        
        //Store temp in tempWritable
        tempWritable.set(temp);
        
        //Emit Year and the average rating in tempWritable to the Reducer class
        context.write(ReleaseYear, tempWritable);
        
        
    }

}

减速机代码：

public class AverageRatingReducer extends Reducer<Text, DoubleWritable, Text, DoubleWritable>
{
    //Create an arraylist of type double called ratingList
    ArrayList<Double> ratingList = new ArrayList<Double>();
    
    //Override reduce method
    @Override
    //reduce takes in thre parameters
    public void reduce(Text key, Iterable<DoubleWritable> values, Context context)
            throws IOException, InterruptedException
    {
        //create a variable SumofRatings of type double and initialize it to 0
        double SumofRating = 0.0;
        
        //use a for loop to store ratings in the ratingList array and sum the ratings in the SumofRatings variable
        for(DoubleWritable value : values)
        {
            ratingList.add(value.get());
            
            //calculate the cumulative sum
            SumofRating = SumofRating + value.get();
            
        }
        
        //get the number of rating in the arrayList
        int size = ratingList.size();
        
        //calculate the average rating
        double averageRating = SumofRating/size;
        
        //Emit the year and the average rating to the output file
        context.write(key, new DoubleWritable(averageRating));
    }
 
}

和主类：

public class AverageRating 
{
    
    public static void main(String[] args) throws Exception
    {
        //Create an object, conf, from the configuration class
        Configuration conf = new Configuration();
        if (args.length != 3)
        {
            System.err.println("Usage: MeanTemperature <input path> <output path>");
            System.exit(-1);
        }
        
        //create an object, job,  from the Job class
        Job job;
        
        //configure the parameters for the job
        job = Job.getInstance(conf, "Average Rating");
        
        //specify the driver class in the JAR file
        job.setJarByClass(AverageRating.class);
        
        
        //setting the input and output paths for the job
        FileInputFormat.addInputPath(job, new Path(args[1]));
        FileOutputFormat.setOutputPath(job, new Path(args[2]));
        
        //Set the mapper and reducer for the job
        job.setMapperClass(AverageRatingMapper.class);
        job.setReducerClass(AverageRatingReducer.class);
        
        //Set the key class (Text) and value class (DoubleWritable) for te job output data
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(DoubleWritable.class);
        
        //Delete output if it exists
        FileSystem hdfs = FileSystem.get(conf);
        Path outputDir = new Path(args[2]);
        if(hdfs.exists(outputDir))
        {
            hdfs.delete(outputDir, true);
        }
        
        System.exit(job.waitForCompletion(true) ? 0 : 1);
        
    }

}

要求的数据样本：

注意：还有更多的列。我刚刚添加了重要的

结果在第一年显示正确，但第二年和第三年完全不准确。

• 1911 6.9
• 1912 5.25
• 1913 2.2

有人可以帮我吗！