val a = List(1,2,3,4,5,6,7,8)
a: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8)

a.sliding(3,2).foreach(println)
List(1, 2, 3)
List(3, 4, 5)
List(5, 6, 7)
List(7, 8)

a.sliding(3,1).foreach(println)
List(1, 2, 3)
List(2, 3, 4)
List(3, 4, 5)
List(4, 5, 6)
List(5, 6, 7)
List(6, 7, 8)

a.grouped(3).foreach(println)
List(1, 2, 3)
List(4, 5, 6)
List(7, 8)

def sliding(size: Int, step: Int): Iterator[C] 
def grouped(size: Int): Iterator[C]

sliding 滑动窗口 
size 窗口大小
step 步长