本篇内容介绍了“mapPartitions的简单介绍及使用方法”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
1. mappartition简介
/** * Return a new RDD by applying a function to each partition of this RDD. * * `preservesPartitioning` indicates whether the input function preserves the partitioner, which * should be `false` unless this is a pair RDD and the input function doesn't modify the keys. */ def mapPartitions[U: ClassTag]( f: Iterator[T] => Iterator[U], preservesPartitioning: Boolean = false): RDD[U] = withScope { val cleanedF = sc.clean(f) new MapPartitionsRDD( this, (_: TaskContext, _: Int, iter: Iterator[T]) => cleanedF(iter), preservesPartitioning) }
/** * Return a new RDD by applying a function to all elements of this RDD. */ def map[U: ClassTag](f: T => U): RDD[U] = withScope { val cleanF = sc.clean(f) new MapPartitionsRDD[U, T](this, (_, _, iter) => iter.map(cleanF)) }
val a = sc.parallelize(1 to 20, 2)def mapTerFunc(a : Int) : Int = {a*3}val mapResult = a.map(mapTerFunc)println(mapResult.collect().mkString(","))
3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60
3. mappartitions低效用法
val a = sc.parallelize(1 to 20, 2)def terFunc(iter: Iterator[Int]) : Iterator[Int] = {var res = List[Int]()while (iter.hasNext){val cur = iter.next;res.::= (cur*3) ;}res.iterator}val result = a.mapPartitions(terFunc)println(result.collect().mkString(","))
30,27,24,21,18,15,12,9,6,3,60,57,54,51,48,45,42,39,36,33
4. mappartitions高效用法
class CustomIterator(iter: Iterator[Int]) extends Iterator[Int] {
def hasNext : Boolean = {
iter.hasNext
}
def next : Int= {
val cur = iter.next
cur*3
}
}
val result = a.mapPartitions(v => new CustomIterator(v))
println(result.collect().mkString(","))
3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60
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