Spark Transformation —— randomSplit

def randomSplit(weights: Array[Double], seed: Long = Utils.random.nextLong): Array[RDD[T]]

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该函数根据weights权重，将一个RDD切分成多个RDD。该权重参数为一个Double数组,第二个参数为random的种子，基本可忽略。

scala> var rdd = sc.makeRDD(1 to 10,10)
rdd: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[16] at makeRDD at :21

scala> rdd.collect
res6: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)  

scala> var splitRDD = rdd.randomSplit(Array(0.1,0.2,0.3,0.4))
splitRDD: Array[org.apache.spark.rdd.RDD[Int]] = Array(MapPartitionsRDD[17] at randomSplit at :23, 
MapPartitionsRDD[18] at randomSplit at :23, 
MapPartitionsRDD[19] at randomSplit at :23, 
MapPartitionsRDD[20] at randomSplit at :23)

//这里注意：randomSplit的结果是一个RDD数组
scala> splitRDD.size
res8: Int = 4
//由于randomSplit的第一个参数weights中传入的值有4个，因此，就会切分成4个RDD,
//把原来的rdd按照权重0.1,0.2,0.3,0.4，随机划分到这4个RDD中，权重高的RDD，划分到//的几率就大一些。
//注意，权重的总和加起来为1，否则会不正常

scala> splitRDD(0).collect
res10: Array[Int] = Array(1, 4)

scala> splitRDD(1).collect
res11: Array[Int] = Array(3)                                                    

scala> splitRDD(2).collect
res12: Array[Int] = Array(5, 9)

scala> splitRDD(3).collect
res13: Array[Int] = Array(2, 6, 7, 8, 10)