countByKey()

key出现的次数

package com.atguigu

import org.apache.spark.rdd.RDD
import org.apache.spark.{SparkConf, SparkContext}

object Action {
  def main(args: Array[String]): Unit = {
    val conf: SparkConf = new SparkConf().setMaster("local[*]").setAppName("ADCount")

    val sc = new SparkContext(conf)

    val rdd: RDD[(String, Int)] = sc.makeRDD(List(("a",1),("b",2),("a",3),("b",4),("a",5)))
    val stringToLong: collection.Map[String, Long] = rdd.countByKey()
    println(stringToLong)

  }
}

Map(a -> 3, b -> 2)