AverageGPA.java

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.FloatWritable;
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.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class AverageGPA {

    public static class TokenizerMapper
        extends Mapper<Object, Text, Text, FloatWritable>{

        public void map(Object key, Text value, Context context
                        ) throws IOException, InterruptedException {
            String[] record = value.toString().split(",");
            String ID = record[0];
            try {
                Float gpa = Float.parseFloat(record[2]);
                context.write(new Text(ID), new FloatWritable(gpa));
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static class AverageReducer
        extends Reducer<Text, FloatWritable, Text, Text> {

        public void reduce(Text key, Iterable<FloatWritable> values,
                        Context context
                        ) throws IOException, InterruptedException {
            Float total = (float) 0;
            int count = 0;
            try {
                for (FloatWritable var : values) {
                    total += var.get();
                    System.out.println("reducer " + var.get());
                    count++;
                }
                Float avg = (Float) total / count;
                context.write(key, new Text(String.valueOf(avg)));
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf, "Average GPA");
        job.setJarByClass(AverageGPA.class);
        job.setMapperClass(TokenizerMapper.class);
        //job.setCombinerClass(AverageReducer.class);
        job.setReducerClass(AverageReducer.class);

        // Map output key, value types
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(FloatWritable.class);

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