scala flatMap reduceLeft foldLeft

Posted 2020-10-01 牵牛花

object collection_t1 {

  def flatMap1(): Unit = {
    val li = List(1,2,3)
    val res = li.flatMap(x => x match {
      case 3 => List(‘a‘,‘b‘)
      case _ => List(x*2)
    })
    println(res)
  }

  def map1(): Unit = {
    val li = List(1,2,3)
    val res = li.map(x => x match {
      case 3 => List(‘a‘,‘b‘)
      case _ => x*2
    })
    println(res)
  }

  def main(args: Array[String]): Unit = {
    flatMap1()
    map1()
  }
}

result: List(2, 4, a, b) List(2, 4, List(a, b))

flatMap就是在Map的基础上加了压平flatten的功能

foldLeft 从左边起折叠,累加 

https://alvinalexander.com/scala/scala-reduceleft-examples

讲解reduceleft