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Sample Input:

a b cc, c d d c
I Love U.
dd ee f g s sa dew ad da
So shaken as we are, so wan with care.
Find we a time for frighted peace to pant.
And breathe short-winded accents of new broil.
To be commenced in strands afar remote.
I Love U U love i.
i i i i

Sample Output:

a:b 1
a:time 1
a:we 1
accents:of 1
accents:short-winded 1
afar:remote 1
afar:strands 1
and:breathe 1
are:so 1
are:we 1
as:shaken 1
as:we 1
b:cc 1
be:commenced 1
be:to 1
breathe:short-winded 1
broil:new 1
c:cc 1
c:d 2
care:with 1
commenced:in 1
d:d 1
dd:ee 1
dew:sa 1
ee:f 1
f:g 1
find:we 1
for:frighted 1
for:time 1
frighted:peace 1
g:s 1
i:i 3
i:love 3
in:strands 1
love:u 3
new:of 1
pant:to 1
peace:to 1
s:sa 1
shaken:so 1
so:wan 1
u:u 1
wan:with 1

Code:

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.StringTokenizer;

public class CoOccurrence {

public static class TextPair implements WritableComparable {
private Text first;
private Text second;

public TextPair(){
set(new Text(), new Text());
}
public TextPair(String left, String right) {
set(new Text(left), new Text(right));
}
public TextPair(Text left, Text right) {
set(left, right);
}

public void set(Text left, Text right){
String l = left.toString();
String r = right.toString();
int cmp = l.compareTo(r);
if(cmp <= 0){
this.first = left;
this.second = right;
}else{
this.first = right;
this.second = left;
}
}

public Text getFirst() {
return first;
}
public Text getSecond() {
return second;
}

@Override
public void readFields(DataInput in) throws IOException {
}
@Override
public void write(DataOutput out) throws IOException {
first.write(out);
second.write(out);
}
@Override
public int hashCode() {
return first.hashCode() * 163 + second.hashCode();//May be some trouble here. why 163? sometimes 157
}
@Override
public boolean equals(Object o) {
if (o instanceof TextPair) {
TextPair tp = (TextPair) o;
return first.equals(tp.first) && second.equals(tp.second);
}
return false;
}
@Override
public String toString(){
return first + “:” + second;
}
@Override
public int compareTo(TextPair tp) {
int cmp = first.compareTo(tp.first);
if(cmp != 0)
return cmp;
return second.compareTo(tp.second);
}

// A Comparator that com.pares serialized StringPair.
public static class Comparator extends WritableComparator {
private static final Text.Comparator TEXT_COMPARATOR = new Text.Comparator();
public Comparator() {
super(TextPair.class);
}
@Override
public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2){
try {
int firstl1 = WritableUtils.decodeVIntSize(b1[s1]) + readVInt(b1, s1);
int firstl2 = WritableUtils.decodeVIntSize(b2[s2]) + readVInt(b2, s2);
int cmp = TEXT_COMPARATOR.compare(b1, s1, firstl1, b2, s2, firstl2);
if(cmp != 0)
return cmp;
return TEXT_COMPARATOR.compare(b1, s1 + firstl1, l1 – firstl1,
b2, s2 + firstl2, l1 – firstl2);
}catch (IOException e) {
throw new IllegalArgumentException(e);
}
}
}//End of Comparator
static { // register this comparator
WritableComparator.define(TextPair.class, new Comparator());
}

// Compare only the first part of the pair, so that reduce is called once for each value of the first part.
public static class FirstComparator extends WritableComparator {
private static final Text.Comparator TEXT_COMPARATOR = new Text.Comparator();
public FirstComparator() {
super(TextPair.class);
}
@Override
public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2){
try {
int firstl1 = WritableUtils.decodeVIntSize(b1[s1]) + readVInt(b1, s1);
int firstl2 = WritableUtils.decodeVIntSize(b2[s2]) + readVInt(b2, s2);
return TEXT_COMPARATOR.compare(b1, s1, firstl1, b2, s2, firstl2);
}catch (IOException e) {
throw new IllegalArgumentException(e);
}
}
/
@Override
public int compare(WritableComparator a, WritableComparator b) {
if(a instanceof TextPair && b instanceof TextPair)
return ((TextPair)a).first.compareTo(((TextPair)b).first);
return super.compare(a, b);
}
/
}//End of FirstComparator
}//End of TextPair

//Partition based on the first part of the pair.
public static class FirstPartitioner extends Partitioner<TextPair,IntWritable>{
@Override
public int getPartition(TextPair key, IntWritable value, int numPartitions) {
return Math.abs(key.getFirst().toString().indexOf(0) * 127) % numPartitions;//May be some trouble here.
}
}//End of FirstPartitioner

public static class MyMapper extends Mapper<LongWritable, Text, TextPair, IntWritable> {
private final static IntWritable one = new IntWritable(1);
private static Text word0 = new Text();
private static Text word1 = new Text();
private String pattern = “[^a-zA-Z0-9-‘]”;

@Override
public void map(LongWritable inKey, Text inValue, Context context)throws IOException, InterruptedException {
String line = inValue.toString();
line = line.replaceAll(pattern, ” “);
line = line.toLowerCase();
String[] str = line.split(” +”);
for(int i=0; i< str.length-1; i++)
{
word0.set(str[i]);
word1.set(str[i+1]);
TextPair pair = new TextPair(word0, word1);
context.write(pair, one);
}
}
}//End of MapClass
public static class MyReducer extends Reducer<TextPair, IntWritable, TextPair, IntWritable> {
private IntWritable result = new IntWritable();

@Override
public void reduce(TextPair inKey, Iterable inValues, Context context) throws IOException, InterruptedException {
int sum = 0;
for (IntWritable val : inValues) {
sum += val.get();
}
result.set(sum);
context.write(inKey, result);
}
}//End of MyReducer

public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
//if (otherArgs.length != 2) {
//  System.err.println(“Usage: CoOccurrence “);
//  System.exit(2);
//}
Job job = new Job(conf, “Co-Occurrence”);
job.setJarByClass(CoOccurrence.class);

job.setMapperClass(MyMapper.class);
job.setMapOutputKeyClass(TextPair.class);
job.setMapOutputValueClass(IntWritable.class);

job.setCombinerClass(MyReducer.class);

// group and partition by the first int in the pair
//job.setPartitionerClass(FirstPartitioner.class);
//job.setGroupingComparatorClass(FirstGroupingComparator.class);

// the reduce output is Text, IntWritable
job.setReducerClass(MyReducer.class);
job.setOutputKeyClass(TextPair.class);
job.setOutputValueClass(IntWritable.class);