自定义函数：
UDF：
val sparkConf = new SparkConf().setMaster("local[*]" ).setAppName("SQLDemo" )
// 创建 SparkSession 对象
val spark :SparkSession = SparkSession.builder ().config(sparkConf).getOrCreate()
import spark.implicits._
// 读取 json 文件
val df : DataFrame = spark.read.json("Spark-SQL/input/user.json" )
spark.udf.register("addName" ,(x:String)=>"Name:" +x)
df.createOrReplaceTempView("people" )
spark.sql("select addName(username),age from people" ).show()
spark.stop()
UDAF（自定义聚合函数）
强类型的 Dataset 和弱类型的 DataFrame 都提供了相关的聚合函数， 如 count()，
countDistinct()，avg()，max()，min()。除此之外，用户可以设定自己的自定义聚合函数。Spark3.0之前我们使用的是UserDefinedAggregateFunction作为自定义聚合函数，从 Spark3.0 版本后可以统一采用强类型聚合函数 Aggregator
实验需求：计算平均工资
实现方式一：RDD
val sparkconf: SparkConf = new SparkConf().setAppName("app" ).setMaster("local[*]" )
val sc: SparkContext = new SparkContext(conf)
val resRDD: (Int, Int) = sc.makeRDD(List (("zhangsan" , 20), ("lisi" , 30), ("wangw u " ,40))).map {
case (name, salary) => {
(salary, 1)
}
}.reduce {
(t1, t2) => {
(t1._1 + t2._1, t1._2 + t2._2)
}
}
println (resRDD._1/resRDD._2)
// 关闭连接
sc.stop()
实现方式二：弱类型UDAF
class MyAverageUDAF extends UserDefinedAggregateFunction{
def inputSchema: StructType =
StructType (Array (StructField ("salary" ,IntegerType)))
// 聚合函数缓冲区中值的数据类型 (salary,count)
def bufferSchema: StructType = {
StructType (Array (StructField ("sum" ,LongType),StructField ("count" ,LongType)))
}
// 函数返回值的数据类型
def dataType: DataType = DoubleType
// 稳定性：对于相同的输入是否一直返回相同的输出。
def deterministic: Boolean = true
// 函数缓冲区初始化
def initialize(buffer: MutableAggregationBuffer): Unit = {
// 存薪资的总和
buffer(0) = 0L
// 存薪资的个数
buffer(1) = 0L
}
// 更新缓冲区中的数据
def update(buffer: MutableAggregationBuffer,input: Row): Unit = {
if (!input.isNullAt(0)) {
buffer(0) = buffer.getLong(0) + input.getInt(0)
buffer(1) = buffer.getLong(1) + 1
}
}
// 合并缓冲区
def merge(buffer1: MutableAggregationBuffer,buffer2: Row): Unit = {
buffer1(0) = buffer1.getLong(0) + buffer2.getLong(0)
buffer1(1) = buffer1.getLong(1) + buffer2.getLong(1)
}
// 计算最终结果
def evaluate(buffer: Row): Double = buffer.getLong(0).toDouble /
buffer.getLong(1)
}
val sparkconf: SparkConf = new SparkConf().setAppName("app" ).setMaster("local[*]" )
val spark:SparkSession = SparkSession.builder ().config(conf).getOrCreate()
import spark.implicits._
val res :RDD[(String,Int)]= spark.sparkContext.makeRDD(List (("zhangsan" , 20), ("lisi" , 30), ("wangwu" ,40)))
val df :DataFrame = res.toDF("name" ,"salary" )
df.createOrReplaceTempView("user" )
var myAverage = new MyAverageUDAF
// 在 spark 中注册聚合函数
spark.udf.register("avgSalary" ,myAverage)
spark.sql("select avgSalary(salary) from user" ).show()
// 关闭连接
spark.stop()
实现方式三：强类型UDAF
case class Buff(var sum:Long,var cnt:Long)
class MyAverageUDAF extends Aggregator[Long,Buff,Double]{
override def zero: Buff = Buff (0,0)
override def reduce(b: Buff, a: Long): Buff = {
b.sum += a
b.cnt += 1
b
}
override def merge(b1: Buff, b2: Buff): Buff = {
b1.sum += b2.sum
b1.cnt += b2.cnt
b1
}
override def finish(reduction: Buff): Double = {
reduction.sum.toDouble/reduction.cnt
}
override def bufferEncoder: Encoder[Buff] = Encoders.product
override def outputEncoder: Encoder[Double] = Encoders.scalaDouble
}
val sparkconf: SparkConf = new SparkConf().setAppName("app" ).setMaster("local[*]" )
val spark:SparkSession = SparkSession.builder ().config(conf).getOrCreate()
import spark.implicits._
val res :RDD[(String,Int)]= spark.sparkContext.makeRDD(List (("zhangsan" , 20), ("lisi" , 30), ("wangwu" ,40)))
val df :DataFrame = res.toDF("name" ,"salary" )
df.createOrReplaceTempView("user" )
var myAverage = new MyAverageUDAF
// 在 spark 中注册聚合函数
spark.udf.register("avgSalary" ,functions.udaf (myAverage))
spark.sql("select avgSalary(salary) from user" ).show()
// 关闭连接
spark.stop()