package com.xiaomi.data.ctr.feature.analysis

/**
 * Scala极速入门材料，可以直接贴入ScalaIDE的worksheet
 */
object test {
  println("Welcome to the Scala worksheet")       //> Welcome to the Scala worksheet
  //val(ue) 是引用不变，不能改变val值变量的『值』
  val n = 8                                       //> n  : Int = 8
  //n += 1 : value += is not a member of Int

  //var(riable) 是变量，能用val用val，技穷用var
  var nn = 7                                      //> nn  : Int = 7
  nn += 1
  nn                                              //> res0: Int = 8

  //tuple - 使用得非常重的数据结构，同python，但是不能（显式地）按下标取到每个元素
  val t = (1, "a", None)                          //> t  : (Int, String, None.type) = (1,a,None)
  t._1                                            //> res1: Int = 1
  t._2                                            //> res2: String = a
  t._3                                            //> res3: None.type = None
  //纯语法，相信看过就不会忘记的
  val (no, name, score) = t                       //> no  : Int = 1
                                                  //| name  : String = a
                                                  //| score  : None.type = None

  //collections, 取下标用()
  val list = List(1, 2, 3)                        //> list  : List[Int] = List(1, 2, 3)
  list(0)                                         //> res4: Int = 1
  val m = Map(
    "a" -> 1,
    "c" -> 2,
    "b" -> 3,
    "d" -> 4)                                     //> m  : scala.collection.immutable.Map[String,Int] = Map(a -> 1, c -> 2, b -> 3
                                                  //| , d -> 4)
  //取前两个
  m.take(2)                                       //> res5: scala.collection.immutable.Map[String,Int] = Map(a -> 1, c -> 2)
  m("a")                                          //> res6: Int = 1
  //删除一个键，得到一个新的map
  m - "a"                                         //> res7: scala.collection.immutable.Map[String,Int] = Map(c -> 2, b -> 3, d ->
                                                  //| 4)

  //函数：变量名在前、类型在后，函数头到函数体之间有“=”号
  def isPalindrome(str: String) = (str == str.reverse.toString())
                                                  //> isPalindrome: (str: String)Boolean
  //函数：可以显式指定返回值类型，函数的返回值就是最后一行的值
  def isPalindromeDetail(str: String): Boolean = {
    println(str)
    str == str.reverse.toString
  }                                               //> isPalindromeDetail: (str: String)Boolean

  def isPalindromeDetailUn(str: String): Boolean = ???
                                                  //> isPalindromeDetailUn: (str: String)Boolean
  //函数式编程：map/filter/reduce，其它的基本都是变种
  val ab = List(1, 2, 3, 4, 5, 6)                 //> ab  : List[Int] = List(1, 2, 3, 4, 5, 6)
  //每个元素乘3
  ab.map(_ * 3)                                   //> res8: List[Int] = List(3, 6, 9, 12, 15, 18)
  //取出偶数
  ab.filter(_ % 2 == 0)                           //> res9: List[Int] = List(2, 4, 6)
  //reduce实现sum
  ab.reduce(_ + _)                                //> res10: Int = 21
  //reduce实现max
  ab.reduce((x, y) => if (x > y) x else y)        //> res11: Int = 6
}