Hive 简单UDAF开发（extends UDAF）

Hive UDAF（User- Defined Aggregation Funcation）用户自定义聚合函数是一个很好的功能，集成了先进的数据处理。Hive有两种UDAF：简单和通用。顾名思义，简单的UDAF，写的相当简单的，但因为使用Java反射导致性能损失，而且有些特性不能使用，如可变长度参数列表。通用UDAF可以使用​​所有功能，但是UDAF就写的比较复杂，不直观。

1、一下两个包是必须的import org.apache.hadoop.hive.ql.exec.UDAF和 org.apache.hadoop.hive.ql.exec.UDAFEvaluator。

2、函数类需要继承UDAF类，内部类Evaluator实UDAFEvaluator接口。

3、Evaluator需要实现 init、iterate、terminatePartial、merge、terminate这几个函数。

a）init函数实现接口UDAFEvaluator的init函数。

b）iterate接收传入的参数，并进行内部的轮转。其返回类型为boolean。

c）terminatePartial无参数，其为iterate函数轮转结束后，返回轮转数据，terminatePartial类似于hadoop的Combiner。

d）merge接收terminatePartial的返回结果，进行数据merge操作，其返回类型为boolean。

e ） terminate 返回最终的聚集函数结果。

代码示例，用于计算商户星级的平均价格的UDAF

package com.dianping.credit.udaf.avgprice;

import java.util.ArrayList;
import java.util.List;

import org.apache.hadoop.hive.ql.exec.UDAF;
import org.apache.hadoop.hive.ql.exec.UDAFEvaluator;

/**
 * 计算商户的平均价格
 * @author xinchun.wang
 *
 */
public final class AvgPriceUDAF extends UDAF {

    /**
     * The internal state of an aggregation for average.
     *
     * Note that this is only needed if the internal state cannot be represented
     * by a primitive.
     *
     * The internal state can also contains fields with types like
     * ArrayList<String> and HashMap<String,Double> if needed. 初始化点评的平均价格列表
     */
    public static class UDAFAvgPriceState {
        private List<Integer> oldPriceList = new ArrayList<Integer>();
        private List<Integer> newPriceList = new ArrayList<Integer>();

    }

    /**
     * The actual class for doing the aggregation. Hive will automatically look
     * for all internal classes of the UDAF that implements UDAFEvaluator.
     */
    public static class UDAFAvgPriceEvaluator implements UDAFEvaluator {

        UDAFAvgPriceState state;

        public UDAFAvgPriceEvaluator() {
            super();
            state = new UDAFAvgPriceState();
            init();
        }

        /**
         * Reset the state of the aggregation.
         */
        public void init() {
            state.oldPriceList = new ArrayList<Integer>();
            state.newPriceList = new ArrayList<Integer>();
        }

        /**
         * Iterate through one row of original data.
         *
         * The number and type of arguments need to the same as we call this
         * UDAF from Hive command line.
         *
         * This function should always return true.
         */
        public boolean iterate(Integer avgPirce, Integer old) {
            if (avgPirce != null) {
                if (old == 1)
                    state.oldPriceList.add(avgPirce);
                else
                    state.newPriceList.add(avgPirce);
            }
            return true;
        }

        /**
         * Terminate a partial aggregation and return the state. If the state is
         * a primitive, just return primitive Java classes like Integer or
         * String.
         */
        public UDAFAvgPriceState terminatePartial() {
            // This is SQL standard - average of zero items should be null.
            return (state.oldPriceList == null && state.newPriceList == null) ? null
                    : state;
        }

        /**
         * Merge with a partial aggregation.
         *
         * This function should always have a single argument which has the same
         * type as the return value of terminatePartial().
         *
         * 合并点评平均价格列表
         */
        public boolean merge(UDAFAvgPriceState o) {
            if (o != null) {
                state.oldPriceList.addAll(o.oldPriceList);
                state.newPriceList.addAll(o.newPriceList);
            }
            return true;
        }

        /**
         * Terminates the aggregation and return the final result. 计算并返回商户平均价格
         */
        public Integer terminate() {
            // This is SQL standard - average of zero items should be null.
            Integer avgPirce = 0;
            if (state.oldPriceList.size() >= 8
                    && state.newPriceList.size() >= 12) {
                avgPirce = (CalcAvgPriceUtil.calcInterquartileMean(state.oldPriceList) * 2
                        + CalcAvgPriceUtil.calcInterquartileMean(state.newPriceList) * 8) / 10;
            } else {
                state.newPriceList.addAll(state.oldPriceList);
                avgPirce = CalcAvgPriceUtil.calcInterquartileMean(state.newPriceList);
            }
            return avgPirce == 0 ? null : avgPirce;
        }
    }

    private AvgPriceUDAF() {
        // prevent instantiation
    }

}

参考文档：

http://svn.apache.org/viewvc/hive/trunk/contrib/src/java/org/apache/hadoop/hive/contrib/udaf/example/UDAFExampleAvg.java?view=markup

UDAF的使用

同UDF一样，编译好jar包后，在Hive中执行

add jar /data/deploy/honesty_online/shop_avgprice/avgprice.jar;

CREATE TEMPORARY FUNCTION calc_avgprice AS 'com.dianping.credit.udaf.AvgPriceUDAF';

SELECT
        A.shopid,
        calc_avgprice(A.avgprice, A.addtime) AS shop_avgprice,
        '$cal_dt' as hp_statdate
    FROM dpstg_credit_shop_avgprice_review_list A
    INNER JOIN dpstg_credit_shop_tuan_avgprice B ON A.shopid = B.shopid
    WHERE B.no_tuan_review_count >= 5 AND A.tuan_review = 0
    GROUP BY A.shopid