Hack#38

Average.java

package org.hadoophacks.hive;
import org.apache.hadoop.hive.serde2.io.DoubleWritable;
import org.apache.hadoop.io.IntWritable;;
import org.apache.hadoop.hive.ql.exec.*;

public class Average extends UDAF{

    /**
     *
     *途中計算結果を格納しておくクラス
     *
     */
    public static class TempResult{
	private DoubleWritable sum = new DoubleWritable(0);
	private IntWritable num = new IntWritable(0);
    
	public DoubleWritable getSum(){
	    return this.sum;
	}
	public IntWritable getNum(){
	    return this.num;
	}
	public void addSum(double value){
	    sum.set(sum.get() + value);
	}
	public void addNum(int value){
	    num.set(num.get() + value);
	}
    }
    
    public static class AverageEvaluator implements UDAFEvaluator{

	private TempResult tempResult;

	public void init(){
	    //有効な値が１件も無かった場合のために、nullで初期化しておく。
	    tempResult = null;
	}

	public boolean iterate(DoubleWritable value){
	    if(tempResult == null){
		tempResult = new TempResult();
	    }
	    
	    tempResult.addSum(value.get());
	    tempResult.addNum(1);
	    
	    return true;
	}

	public TempResult terminatePartial(){
	    return tempResult;
	}

	public boolean merge(TempResult otherTemp){

	    if(tempResult == null){
		tempResult = otherTemp;
	    }

	    else if(otherTemp != null){

		double sum = otherTemp.getSum().get();
		int num = otherTemp.getNum().get();

		tempResult.addSum(sum);
		tempResult.addNum(num);
	    }
	    return true;
	}

	public DoubleWritable terminate(){
	    double sum = tempResult.getSum().get();
	    int num = tempResult.getNum().get();
	    
	    return new DoubleWritable(sum/num);
	}
    }
}