Hadoop streaming python word count example

1. In class we wrote a MapReduce program in Java to compute the word counts for any given input. In this assignment, you will repeat solving the same problem but using Hadoop streaming.

2. Create two scripts in Python namely wordcount_map.py and wordcount_reduce.py to be used by the mappers and reducers of the streaming job.

3. Your script files must be executable (consider chmod command), and must include the necessary shebang (like in the attached script files).

4. Attached are the script files we used in class to demonstrate Hadoop streaming, namely: maxtemp_map.py and maxtemp_reduce.py. They can help you to get started.

5. Recall the streaming command:

$ mapred streaming \

-files , \

-mapper \

-reducer \

-input \

-output

(extra options: -combiner, -numReduceTasks, etc.)

MaxTemperature Example file is the program file discussed in Class.

Mapper for the Maximum temperature Example:

import java.io.IOException;

import org.apache.hadoop.io.IntWritable;

import org.apache.hadoop.io.LongWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapreduce.Mapper;

public class MaxTemperatureMapper

extends Mapper {

private static final int MISSING = 9999;

@Override

public void map(LongWritable key, Text value, Context context)

throws IOException, InterruptedException {

String line = value.toString();

String year = line.substring(15, 19);

int airTemperature;

if (line.charAt(87) == '+') { // parseInt doesn't like leading plus signs

airTemperature = Integer.parseInt(line.substring(88, 92));

} else {

airTemperature = Integer.parseInt(line.substring(87, 92));

}

String quality = line.substring(92, 93);

if (airTemperature != MISSING && quality.matches("[01459]")) {

context.write(new Text(year), new IntWritable(airTemperature));

}

}

}

Reducer for the max temperature example

import java.io.IOException;
import org.apache.hadoop.io.IntWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapreduce.Reducer;

public class MaxTemperatureReducer

extends Reducer {

@Override

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

throws IOException, InterruptedException {

int maxValue = Integer.MIN_VALUE;

for (IntWritable value : values) {

maxValue = Math.max(maxValue, value.get());

}

context.write(key, new IntWritable(maxValue));

}

}

Application to find the maximum temperature in the weather dataset

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.lib.input.FileInputFormat;

import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class MaxTemperature {

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

if (args.length != 2) {

System.err.println("Usage: MaxTemperature

");

System.exit(-1);

}

Job job = new Job();

job.setJarByClass(MaxTemperature.class);

job.setJobName("Max temperature");

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

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

job.setMapperClass(MaxTemperatureMapper.class);

job.setReducerClass(MaxTemperatureReducer.class);

job.setOutputKeyClass(Text.class);

job.setOutputValueClass(IntWritable.class);

System.exit(job.waitForCompletion(true) ? 0 : 1);