map

package week5

object map {
  def mapFun[T, U](xs: List[T], f: T => U): List[U] =
    (xs foldRight List[U]())(f(_)::_)             //> mapFun: [T, U](xs: List[T], f: T => U)List[U]

    val nums = List(4,5,5,9)                      //> nums  : List[Int] = List(4, 5, 5, 9)
    mapFun[Int,Int](nums, _+1)                    //> res0: List[Int] = List(5, 6, 6, 10)



// deconstruc a list with a pair
  def lengthFun[T](xs: List[T]): Int =
    (xs foldRight 0)((_,y)=>1+y)                  //> lengthFun: [T](xs: List[T])Int

    lengthFun(nums)                               //> res1: Int = 4

    val s = "Hello You"                           //> s  : String = Hello You
    s map (c=> List(".",c))                       //> res2: scala.collection.immutable.IndexedSeq[List[Any]] = Vector(List(., H),
                                                  //| List(., e), List(., l), List(., l), List(., o), List(.,  ), List(., Y), List
                                                  //| (., o), List(., u))
    s flatMap (c=> List(".",c))                   //> res3: scala.collection.immutable.IndexedSeq[Any] = Vector(., H, ., e, ., l,
                                                  //| ., l, ., o, .,  , ., Y, ., o, ., u)

    val ss = Set(4,5,54,4, "roto")                //> ss  : scala.collection.immutable.Set[Any] = Set(4, 5, 54, roto)

     ss filter (x=> x.isInstanceOf[Int])          //> res4: scala.collection.immutable.Set[Any] = Set(4, 5, 54)
}