Hadoop 101 - Reducer Iterator to Arraylist

iterator_to_arraylist.java

import java.io.IOException;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mapreduce.Reducer;
import java.util.List;
import java.util.ArrayList;

public class CosineReducer2 extends Reducer<Text, Text, Text, IntWritable> {
            
	// Reduce task ----------------------------------------------------------------
    public void reduce(Text key, Iterable<Text> values, Context context) 
    		  throws IOException, InterruptedException {
    	  
    	// Input looks like:  User1 (App1,0.333 App2,0.444 App3,0.555)   	
    	List<String> vArrayList = new ArrayList<String>();
    	
    	for(Text v : values) {
    		vArrayList.add(v.toString());
    	}
 
    	for(int i=0; i < vArrayList.size(); i++) {
    		for(int j=i+1; j < vArrayList.size(); j++){
            	// Output looks like: App1,0.333:App2,0.444 1
        		//                    App1,0.333:App3,0.555 1
        		//                    App2,0.444:App3:0.555 1
    			
    			// App1 should always come before App2, so that (App1,App2) is the same as (App2,App1)
    			if(vArrayList.get(i).compareTo(vArrayList.get(j)) < 0){
    				context.write(new Text(vArrayList.get(i) + ":" + vArrayList.get(j)), new IntWritable(1));
    			}
    			else context.write(new Text(vArrayList.get(j) + ":" + vArrayList.get(i)), new IntWritable(1)); 			
        	}
        }
    }
}