scala中的foldLeft、foldRight

fold, foldLeft, and foldRight之間的區別
　　主要的區別是fold函數操作遍歷問題集合的順序。foldLeft是從左開始計算，然後往右遍歷。foldRight是從右開始算，然後往左遍歷。而fold遍歷的順序沒有特殊的次序。 

case class Foo(val name: String, val age: String, val sex: String)

Object Test{

def main(args:Array[String]){
val array = ArrayBuffer[Foo]()
    array.append(Foo("Hugh Jass", "25", "male"))
    array.append(Foo("Biggus Dickus", "43", "male"))
    val stringList = array.foldLeft(List[String]()) { (z, f) =>
      val title = f.sex match {
        case  "male" => "Mr."
        case  "female" => "Ms."
      }
      z :+ s"$title ${f.name}, ${f.age}"
    }


    println("stringList:" + stringList(0))
}
}

 

 

//伴生類 
class Foo(val name: String, val age: Int, val sex: Symbol)

 //伴生對象
object Foo {
  def apply(name: String, age: Int, sex: Symbol) = new Foo(name, age, sex)
} 

Object Test{

def main(args:Array[String]){
 
  val fooList =
      Foo("Hugh Jass", 25, 'male) ::
        Foo("Biggus Dickus", 43, 'male) ::
        Foo("Incontinentia Buttocks", 37, 'female) ::
        Nil


    val stringList1 = fooList.foldRight(List[String]()) { (z, f) =>
      val title = z.sex match {
        case 'male => "Mr."
        case 'female => "Ms."
      }
      f :+ s"$title ${z.name}, ${z.age}"
    }

    println("stringList1:" + stringList1(0))

}
}