学习scala笔记--19 常见高阶函数

 

 

 

 

map()  是个高阶函数

 

Array.map()   接收 函数作为参数   对集合的每个值  调用这个函数

 

scala> val a = Array(1,2,3,4,5,6,7,8,9)

a: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9)

 

scala> a.map(x => x*x)

res12: Array[Int] = Array(1, 4, 9, 16, 25, 36, 49, 64, 81)

 

scala> 

 

scala> a.map(_ * 2)

res13: Array[Int] = Array(2, 4, 6, 8, 10, 12, 14, 16, 18)

 

 

完整的写法

scala> a.map((x:Int) => x+1)

res17: Array[Int] = Array(2, 3, 4, 5, 6, 7, 8, 9, 10)

 

 

 

 

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filter() 是个高阶函数

 

 

scala> a.filter(x => x>4)

res23: Array[Int] = Array(5, 6, 7, 8, 9)

 

scala> 

 

scala> a.filter(_ > 4)

res24: Array[Int] = Array(5, 6, 7, 8, 9)

 

scala> a.filter(_ > 4).foreach(println)

5

6

7

8

9

 

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reduce() 

 

scala> val a = Array(1,2,3,4,5,6,7,8,9,10)

a: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

 

scala> a.reduce((sum,n)=> sum+n)

res0: Int = 55

 

 

scala> a.reduce(_ + _)

res15: Int = 55

 

scala> a.reduce(_ - _)

res16: Int = -53

 

 

scala> a.reduceLeft(_ + _)

res18: Int = 55

 

scala> a.reduceRight(_ + _)

res19: Int = 55

 

 

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sortWith()

 

 

scala> val  a = Array(9,1,8,2,7,3,6,5,4)

a: Array[Int] = Array(9, 1, 8, 2, 7, 3, 6, 5, 4)

 

scala> a.sortWith(_ > _)

res13: Array[Int] = Array(9, 8, 7, 6, 5, 4, 3, 2, 1)

 

scala> a.sortWith(_ < _)

res14: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9)

 

 

 

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