scala之scan函数

scala之scan函数 函数scan

​ 同fold，scan把每一步的计算结果放到一个新的集合中返回，flod返回的是最后的结果

格式

def scan[B >: Int, That](z: B)(op: (B, B) => B)(implicit cbf: scala.collection.generic.CanBuildFrom[Array[Int],B,That]): That
def scan[B >: Int, That](z: B)(op: (B, B) => B)(implicit cbf: scala.collection.generic.CanBuildFrom[scala.collection.mutable.WrappedArray[Int],B,That]): That

数据

val a=Array(1,2,3,4,5)

scala> a.scan(0)((x,y)=>{println(x,y,x+y);x+y})
(0,1,1)
(1,2,3)
(3,3,6)
(6,4,10)
(10,5,15)
res121: Array[Int] = Array(0, 1, 3, 6, 10, 15)

函数scanLeft

格式

def scanLeft[B, That](z: B)(op: (B, Int) => B)(implicit bf: scala.collection.generic.CanBuildFrom[Array[Int],B,That]): That
def scanLeft[B, That](z: B)(op: (B, Int) => B)(implicit bf: scala.collection.generic.CanBuildFrom[scala.collection.mutable.WrappedArray[Int],B,That]): That

scala> a.scanLeft(5)((x,y)=>{println(x,y,x+y);x+y})
(5,1,6)
(6,2,8)
(8,3,11)
(11,4,15)
(15,5,20)
res122: Array[Int] = Array(5, 6, 8, 11, 15, 20)

函数scanRight

格式

def scanRight[B, That](z: B)(op: (Int, B) => B)(implicit bf: scala.collection.generic.CanBuildFrom[Array[Int],B,That]): That
def scanRight[B, That](z: B)(op: (Int, B) => B)(implicit bf: scala.collection.generic.CanBuildFrom[scala.collection.mutable.WrappedArray[Int],B,That]): That

scala> a.scanRight(0)((x,y)=>{println(x,y,x+y);x+y})
(5,0,5)
(4,5,9)
(3,9,12)
(2,12,14)
(1,14,15)
res125: Array[Int] = Array(15, 14, 12, 9, 5, 0)