标签：apache cti code ova min 运算 alt key agg
aggregate函数将每个分区里面的元素进行聚合，然后用combine函数将每个分区的结果和初始值(zeroValue)进行combine操作。这个函数最终返回的类型不需要和RDD中元素类型一致。
def aggregate[U: ClassTag](zeroValue: U)(seqOp: (U, T) => U, combOp: (U, U) => U): Uscala> val rdd = sc.parallelize(List(18,28,7,66,-19,100,29,55,4),3) rdd: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[2] at parallelize at <console>:24 //先对分区内的元素进行聚合； scala> def InnerCom(a:Int, b:Int) : Int = { | println("InnerCom: " + a + " : " + b) | math.min(a,b) | } InnerCom: (a: Int, b: Int)Int //对聚合后的分区之间进行聚合 scala> def partitionCom(a:Int, b:Int): Int = { | println("partitionCom: " + a + " : " + b) | a + b | } partitionCom: (a: Int, b: Int)Int //3个分区，min(分区1)=7,min(分区2)=-19,min(分区1)=4 //50 + 7 + -19 + 4 = 42 scala> rdd.aggregate(50)(InnerCom,partitionCom) InnerCom: 50 : 18 InnerCom: 18 : 28 InnerCom: 18 : 7 partitionCom: 50 : 7 InnerCom: 50 : 66 InnerCom: 50 : -19 InnerCom: -19 : 100 partitionCom: 57 : -19 InnerCom: 50 : 29 InnerCom: 29 : 55 InnerCom: 29 : 4 partitionCom: 38 : 4 res5: Int = 42
标签：apache cti code ova min 运算 alt key agg
原文地址：http://www.cnblogs.com/gaohuajie/p/7494894.html
