Spark算子：RDD基本转换操作(4)–union、intersection、subtract

关键字：Spark算子、Spark RDD基本转换、union、intersection、subtract

union

def union(other: RDD[T]): RDD[T]

该函数比较简单，就是将两个RDD进行合并，不去重。

scala> var rdd1 = sc.makeRDD(1 to 2,1)
rdd1: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[45] at makeRDD at :21

scala> rdd1.collect
res42: Array[Int] = Array(1, 2)

scala> var rdd2 = sc.makeRDD(2 to 3,1)
rdd2: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[46] at makeRDD at :21

scala> rdd2.collect
res43: Array[Int] = Array(2, 3)

scala> rdd1.union(rdd2).collect
res44: Array[Int] = Array(1, 2, 2, 3)

intersection

def intersection(other: RDD[T]): RDD[T]
def intersection(other: RDD[T], numPartitions: Int): RDD[T]
def intersection(other: RDD[T], partitioner: Partitioner)(implicit ord: Ordering[T] = null): RDD[T]

该函数返回两个RDD的交集，并且去重。
参数numPartitions指定返回的RDD的分区数。
参数partitioner用于指定分区函数

scala> var rdd1 = sc.makeRDD(1 to 2,1)
rdd1: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[45] at makeRDD at :21

scala> rdd1.collect
res42: Array[Int] = Array(1, 2)

scala> var rdd2 = sc.makeRDD(2 to 3,1)
rdd2: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[46] at makeRDD at :21

scala> rdd2.collect
res43: Array[Int] = Array(2, 3)

scala> rdd1.intersection(rdd2).collect
res45: Array[Int] = Array(2)

scala> var rdd3 = rdd1.intersection(rdd2)
rdd3: org.apache.spark.rdd.RDD[Int] = MapPartitionsRDD[59] at intersection at :25

scala> rdd3.partitions.size
res46: Int = 1

scala> var rdd3 = rdd1.intersection(rdd2,2)
rdd3: org.apache.spark.rdd.RDD[Int] = MapPartitionsRDD[65] at intersection at :25

scala> rdd3.partitions.size
res47: Int = 2

subtract

def subtract(other: RDD[T]): RDD[T]
def subtract(other: RDD[T], numPartitions: Int): RDD[T]
def subtract(other: RDD[T], partitioner: Partitioner)(implicit ord: Ordering[T] = null): RDD[T]

该函数类似于intersection，但返回在RDD中出现，并且不在otherRDD中出现的元素，不去重。
参数含义同intersection

scala> var rdd1 = sc.makeRDD(Seq(1,2,2,3))
rdd1: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[66] at makeRDD at :21

scala> rdd1.collect
res48: Array[Int] = Array(1, 2, 2, 3)

scala> var rdd2 = sc.makeRDD(3 to 4)
rdd2: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[67] at makeRDD at :21

scala> rdd2.collect
res49: Array[Int] = Array(3, 4)

scala> rdd1.subtract(rdd2).collect
res50: Array[Int] = Array(1, 2, 2)

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