作用

作用:只对Value进行操作

案例

每个value前面添加个前缀

import org.apache.spark.rdd.RDD
import org.apache.spark.{SparkConf, SparkContext}
object demo {
  def main(args: Array[String]): Unit = {
    val conf: SparkConf = new SparkConf().setAppName("SparkCoreTest").setMaster("local[*]")
    val sc: SparkContext = new SparkContext(conf)
    val rdd: RDD[(Int, String)] = sc.makeRDD(List((1, "a"), (1, "d"), (2, "b"), (3, "c")))
    val newRDD: RDD[(Int, String)] = rdd.mapValues("|||" + _) //对value前面添加三个 |||
    newRDD.collect().foreach(println)
    /* 输出
          (1,|||a)
          (1,|||d)
           (2,|||b)
          (3,|||c)
    */
    sc.stop()
  }
}