Scala高阶函数

object TopLevelFunction {
  def main(args: Array[String]): Unit = {
    //map函数，所有集合类型都存在map函数
    //Array类型
    Array("spark", "scala", "hadoop", "flink").map(_ * 2).foreach(println(_))
    //List类型
    List((1, "spark"), (2, "hadoop"), (3, "hive")).map(x => x._1).foreach(println(_))
    List((1, "spark"), (2, "hadoop"), (3, "hive")).map(_._1).foreach(println(_))
    List((1, "spark"), (2, "hadoop"), (3, "hive")).map(_._2).foreach(println(_))
    //Map类型
    Map("spark" -> 1, "hadoop" -> 2, "flume" -> 3).map(_._1)
    println("=" * 40)

    //flatMap函数，相当于flatten+map，先执行map再执行flatten
    List(List(1, 2, 3), List(2, 3, 4)).flatMap(x => x).foreach(x => print(x + " "))
    println()
    println("=" * 40)

    //filter函数
    Array(2, 1, 5, 3, 7, 5, 9).filter(_ > 4).foreach(x => print(x + " "))
    println()
    List("List", "Set", "Array").filter(_.length > 3).foreach(x => print(x + " "))
    println()
    Map("spark" -> 3, "hive" -> 5, "hadoop" -> 7).filter(_._2 > 3).foreach(x => print(x + " "))
    println()
    println("=" * 40)

    //reduce函数
    println(Array(1, 2, 3, 4, 5).reduce(_ + _))
    println(List("hadoop", "spark", "hive").reduce(_ + _))
    Array(1, 2, 3, 4, 5).reduce((x, y) => {
      println(x, y)
      x + y
    })
    Array(1, 2, 3, 4, 5).reduceLeft((x, y) => {
      println(x, y)
      x + y
    })
    Array(1, 2, 3, 4, 5).reduceRight((x, y) => {
      println(x, y)
      x + y
    })
    println("=" * 40)

    //fold函数
    Array(1, 2, 3, 4, 5).foldLeft(0)((x, y) => {
      println(x, y)
      x + y
    })
    println("*" * 20)
    Array(1, 2, 3, 4, 5).foldRight(10)((x, y) => {
      println(x, y)
      x + y
    })
    println(Array(1, 2, 3, 4, 5).foldLeft(0)(_ + _))
    println(Array(1, 2, 3, 4, 5).foldRight(10)(_ + _))
    println("=" * 40)

    //scan函数
    ////从左扫描，每步的结果都保存起来，执行完成后生成数组
    val result = Array(1, 2, 3, 4, 5).scanLeft(0)((x, y) => {
      println(x, y)
      x + y
    })
    println("*" * 20)
    //值为true,说明result是一个Int型的Array数组
    println(result.isInstanceOf[Array[Int]])
    for (i <- result) print(i + " ")
    println()
    println("*" * 20)
    //从右扫描，每步的结果都保存起来，执行完成后生成数组
    val result2 = Array(1, 2, 3, 4, 5).scanRight(0)((x, y) => {
      println(x, y)
      x + y
    })
    for (i <- result2) print(i + " ")
  }

}