2020-11-22-Scala-35(扁平化)

call-by-value call-by-name

传值调用（call-by-value）：先计算参数表达式的值，再应用到函数内部；
传名调用（call-by-name）：将未计算的参数表达式直接应用到函数内部

辨析flatmap flatten map

(实际上并没有切)

   var array = Array[Array[String]](Array("fsg"),Array("ssgs"))
     //不支持flatmap
     
     var st = Array[String]("sdg","fssgrhrhj")
     st.flatMap(_.split(" ")).foreach(println)//sdg  fssgrhrhj
     var result: Array[String] =  st.flatMap(_.split(" "))

  var array = Array[Array[String]](Array("fsg"), Array("ssgs"))
    val stringses1: Array[Array[String]] = array.flatMap(data => data.map(_.split("")))
    val stringses: Array[String] = array.flatMap(data => data.flatMap(_.split("")))
    //注意数组 和 集合
    var st1 = Array[String]("ABCD", "abcd")
    st1.flatMap(_.split("")).foreach(println)
    st1.toList.flatMap(_.split("")).foreach(println)
    val array1: Array[List[String]] = array.map(_.toList)
    array1.toList.foreach(println)

(辨析扁平化操作)

object Test2 {
  def main(args: Array[String]): Unit = {
    val array = Array[String]("sdff fsewfgsgfsg ggg", "etwf wet tgwt tgwg")
    //任然时候数组形式存在
    val stringses: Array[Array[String]] = array.map(_.split(" "))
    //扁平化操作
    val flatten: Array[Char] = array.flatten
    // println(flatten.toList)
    array.map(_.split(" ")).flatten.toList.foreach(println)

    //等价于flatmap算子
    array.flatMap(_.split(" ")).toList.foreach(println)

    //flatten只进行一次扁平操作
    val stringses1: Array[Array[String]] = array.map(_.split(" "))
    val flatten1: Array[String] = stringses1.flatten
    val flatten2: Array[Char] = flatten1.flatten
    //等价于flatmap算子
    //把全部的array添加到array(array)中
    array.flatMap(data => {
      val strings: Array[String] = data.split(" ")
      println(strings.toList)
      println(strings.mkString(","))
      strings
    }).toList.foreach(println)
  }
}

object Test1 {
  def main(args: Array[String]): Unit = {
       var list  = List[String]("a,b,c,d","e,f,g")
       list.flatMap(_.split(",")).foreach(println)  //先进行map 进行对每一个部分"," 切分,之后进行扁平化(把List(Array)=>List(String))
       list.map(_.split(",")).foreach(println)  //List(Array)类型  地址值
       val stringses = list.map(_.split(","))
       for (index <- stringses){
            println(index.mkString(","))
       }
       list.flatten.foreach(println)//包含","没有进行切分
  }
}