Map Reduce Filter records

Question

I have set of records where i need to process only male records,in map reduce program i have used if condition to filter only male records.but below program giving zero records as output.

Input file:

1,Brandon Buckner,avil,female,525
2,Veda Hopkins,avil,male,633
3,Zia Underwood,paracetamol,male,980
4,Austin Mayer,paracetamol,female,338
5,Mara Higgins,avil,female,153
6,Sybill Crosby,avil,male,193
7,Tyler Rosales,paracetamol,male,778
8,Ivan Hale,avil,female,454
9,Alika Gilmore,paracetamol,female,833
10,Len Burgess,metacin,male,325

Mapreduce Program:

package org.samples.mapreduce.training;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
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.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.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;


public class patientrxMR_filter {

    public static class MapDemohadoop extends
            Mapper<LongWritable, Text, Text, IntWritable> {

        // setup , map, run, cleanup

        public void map(LongWritable key, Text value, Context context)
                throws IOException, InterruptedException {
            String line = value.toString();
            String[] elements = line.split(",");



String gender =elements[3];


if ( gender == "male" ) {

    Text tx = new Text(elements[2]);
                int i = Integer.parseInt(elements[4]);
                IntWritable it = new IntWritable(i);
                context.write(tx, it);
}
        }
    }

    public static class Reduce extends
            Reducer<Text, IntWritable, Text, IntWritable> {

        // setup, reduce, run, cleanup
        // innput - para [150,100]
        public void reduce(Text key, Iterable<IntWritable> values,
                Context context) throws IOException, InterruptedException {
            int sum = 0;
            for (IntWritable val : values) {
                sum += val.get();
            }
            context.write(key, new IntWritable(sum));
        }
    }

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

        if (args.length != 2) {
            System.err.println("Insufficient args");
            System.exit(-1);
        }
        Configuration conf = new Configuration();

        //conf.set("fs.default.name","hdfs://localhost:50000");
        conf.set("mapred.job.tracker", "hdfs://localhost:50001");

//      conf.set("DrugName", args[3]);
        Job job = new Job(conf, "Drug Amount Spent");

        job.setJarByClass(patientrxMR_filter.class); // class conmtains mapper and
                                                // reducer class

        job.setMapOutputKeyClass(Text.class); // map output key class
        job.setMapOutputValueClass(IntWritable.class);// map output value class
        job.setOutputKeyClass(Text.class); // output key type in reducer
        job.setOutputValueClass(IntWritable.class);// output value type in
                                                    // reducer

        job.setMapperClass(MapDemohadoop.class);
        job.setReducerClass(Reduce.class);
        job.setNumReduceTasks(1);
        job.setInputFormatClass(TextInputFormat.class); // default -- inputkey
                                                        // type -- longwritable
                                                        // : valuetype is text
        job.setOutputFormatClass(TextOutputFormat.class);



        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        job.waitForCompletion(true);

    }

}

Answer 1

if ( gender == "male" ) 

This line doesn't work for equality check, For equality in java pls use object.equals()

i.e 
if ( gender.equals("male") )

Answer 2

public void map(LongWritable key, Text value, Context context)
throws IOException, InterruptedException {
String line = value.toString();
String[] elements = line.split(",");

Hadoop is using distributed file system, in "String line = value.toString();" line is the file content in block which has a offset (key). In this case the, the line loads the entire test file, which apparently can fit into one block, instead of each line in the file as you expected.