Hadoop mapper writes directly to ouput. (Reducer writes mapper's output)

Question

I have the following code in hadoop and when it runs it produces the output of the mapper as the output of the reducer. The reducer basically does nothing. The 2 input files are in the form:

File A: Jan-1 #starwars,17115 (Each line is like this one.) VALUE is the number 17115.

File B: #starwars,2017/1/1 5696 (Each line is like this one.) VALUE is the number 5696.

Mapper class processes these file and outputs(only the bold letters) :

JAN #STARWARS 17115/A where KEY: JAN #STARWARS

JAN #STARWARS 5696/B where KEY: JAN #STARWARS

The reducer is supposed to do the following:

All the same keys go to one reducer, correct me if i'm wrong i'm new to hadoop and each reducer splits the value to 2 parts : the key and the value

KEY: A, VALUE 17115

KEY: B, VALUE 5696

For the moment it should just adds all the values without caring if it's coming from A or B and writes(only bold):

JAN #STARWARS 22.811 (22.811 = 17115+5696)

So why does it write the mappers output without the reducer doing what it is supposed to do? I din't set the num of reducer to zero.

import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.util.GenericOptionsParser;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
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.input.MultipleInputs;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.Partitioner;

public class WordCount {

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

  //private final static IntWritable result = new IntWritable();
  private Text word = new Text();


public void map(Object key, Text value, Context context
                ) throws IOException, InterruptedException {
  StringTokenizer itr = new StringTokenizer(value.toString(),"\n");
  while (itr.hasMoreTokens()) {

    String nextWord = itr.nextToken().toUpperCase();

    //System.out.println("'"+nextWord+"'");
    if(isFromPlatformB(nextWord)){
    //Procedure for words of Platform B.
        String[] split1 = nextWord.split("(,)|(/)|(\\s)");
        String seriesTitle = split1[0];
        String numOfMonth = split1[2];
        String numOfDay = split1[3];
        String number = split1[4];//VALUE

        int monthInt = Integer.parseInt(numOfMonth);
        String monthString;

        switch (monthInt) {
            case 1:  monthString = "JAN";
                 break;
            case 2:  monthString = "FEB";
                 break;
            case 3:  monthString = "MAR";
                 break;
            case 4:  monthString = "APR";
                 break;
            case 5:  monthString = "MAY";
                 break;
            case 6:  monthString = "JUN";
                 break;
            case 7:  monthString = "JUL";
                 break;
            case 8:  monthString = "AUG";
                 break;
            case 9:  monthString = "SEP";
                 break;
            case 10: monthString = "OCT";
                 break;
            case 11: monthString = "NOV";
                 break;
            case 12: monthString = "DEC";
                 break;
            default: monthString = "ERROR";
                 break;
            }

         //result.set(numberInt);
         word.set(monthString + " " + seriesTitle);
         System.out.println("key: "+monthString + " " + seriesTitle + ",  value: "+number+"/B");
         context.write(word, new Text(number + "/B"));
         //FORMAT : <KEY,VALUE/B>
    }
    else{
         //Procedure for words of Platform A.
         String[] split5 = nextWord.split("(-)|( )|(,)");
         String month = split5[0];
         String seriesTitle = split5[2];
         String value2 = split5[3];//OUTVALUE
         String finalWord = month + " " + seriesTitle;//OUTKEY   KEY: <APR #WESTWORLD>

         word.set(finalWord);
         //result.set(valueInt);
         System.out.println("key: "+finalWord + ",  value: "+value2+"/A");
         context.write(word, new Text(value2 + "/A"));
         //FORMAT : <KEY,VALUE/A>
    } 
  }
}

 /*
 *This method takes the next token and returns true if the token is taken from platform B file,
 *Or it returns false if the token comes from platform A file.
 *
 */
 public boolean isFromPlatformB(String nextToken){
   // B platform has the form of : "#WestWorld ,2017/1/2){
   if(nextToken.charAt(0) == '#'){  
      return true;
   }
   return false;
}
}

  public static class IntSumReducer
   extends Reducer<Text,IntWritable,Text,Text> {
//private IntWritable result = new IntWritable();

public void reduce(Text key, Iterable<Text> values,
                   Context context
                   ) throws IOException, InterruptedException {
  int sum = 0;
  for (Text val : values) {
      String valToString = val.toString();

      String[] split = valToString.split("/");
      //String keyOfValue;
      String valueOfValue;
      int intValueOfValue = 0;

      // FORMAT : <KEY,VALUE/platform>  [<KEY,VALUE>,VALUE = <key,value>]
      //                 [0]      [1]

      if(split.length>1){
             //keyOfValue = split[1];
          valueOfValue = split[0];
          //System.out.println(key);
          //System.out.println(valueOfValue);
          //System.out.println(keyOfValue);
          intValueOfValue = Integer.parseInt(valueOfValue);
          /*if(keyOfValue.equals("A")){//If value is from platform A
              counterForPlatformA += intValueOfValue;
              System.out.println("KEY = 'A' " + "VALUE :"     +intValueOfValue);
              System.out.println("counter A: "+ counterForPlatformA +"||     counter B: "+ counterForPlatformB + "||----||");
          }
          else if(keyOfValue.equals("B")){//If value is from platform B
                 counterForPlatformB += intValueOfValue;
                 System.out.println("KEY = 'B' " + "VALUE :" +intValueOfValue);
                 System.out.println("counter A: "+ counterForPlatformA +"|| counter B: "+ counterForPlatformB + "||----||");
              }
              else{
                    //ERROR
                    System.out.println("Not equal to A or B");
                  }*/

      }
      sum += intValueOfValue;
  }
  context.write(key, new Text(sum));
  }
  }

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

 if (args.length != 3 ){
    System.err.println ("Usage :<inputlocation1> <inputlocation2>   <outputlocation> >");
    System.exit(0);
}
Configuration conf = new Configuration();
String[] files=new GenericOptionsParser(conf,args).getRemainingArgs();
Path input1=new Path(files[0]);
Path input2=new Path(files[1]);
Path output=new Path(files[2]);
//If OUTPUT already exists -> Delete it
FileSystem fs = FileSystem.get(conf);
if(fs.exists(output)){
    fs.delete(output, true);
} 

Job job = Job.getInstance(conf, "word count");
job.setJarByClass(WordCount.class);
job.setMapperClass(TokenizerMapper.class);
job.setCombinerClass(IntSumReducer.class);
job.setReducerClass(IntSumReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(Text.class);
MultipleInputs.addInputPath(job, input1, TextInputFormat.class);
MultipleInputs.addInputPath(job, input2, TextInputFormat.class);
FileOutputFormat.setOutputPath(job, output);
System.exit(job.waitForCompletion(true) ? 0 : 1);

}
}

Answer 1

It looks like your reducer takes in a pair of Text objects and outputs Text. If this is the case, it looks like you have a few problems:

In your main you have:

job.setOutputValueClass(IntWritable.class) which should probably be job.setOutputValueClass(Text.class)

You are also defining your reducer as:

public static class IntSumReducer extends Reducer<Text,IntWritable,Text,Text> it should be public static class IntSumReducer extends Reducer<Text,Text,Text,Text>

The reducer is receiving Text values, not IntWritables.

Answer 2

It was the combiner finally. If you set your reducer as your combiner too then you can't have different types between your mapper and reducer.