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  • 9-1 Array

    scala> val arr = Array(1,2)
    arr: Array[Int] = Array(1, 2)

    map

    //说明
    def map[B, That](f: Int => B)(implicit bf: scala.collection.generic.CanBuildFrom[Array[Int],B,That]): That
    scala> def add(a:Int)={
         |     a * 2
         |   }
    add: (a: Int)Int
    
    scala> arr.map(add)
    res17: Array[Int] = Array(2, 4)

    scala> arr.map(i => math.pow(i,i))  //传递匿名函数
    res28: Array[Double] = Array(1.0, 4.0)

    foreach:[trait] IndexedSeqOptimized

    //说明
    scala> arr.foreach override def foreach[U](f: Int => U): Unit
    scala> arr.foreach(println)
    1
    2

    filter

    //说明
    scala> arr.filter def filter(p: Int => Boolean): Array[Int]
    scala> val arr = Array(1 to 10:_*)
    arr: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
    
    scala> arr.filter(_ % 2 == 0)
    res45: Array[Int] = Array(2, 4, 6, 8, 10)

    reduce:+  等同  reduceLeft

    val res = arr.reduce((a,b) => a+b)  过程如下:
    a  b
    -------------
    1  2
    3  3
    6  4
    10  5
    res:15
        

    reduce:-  等同  reduceLeft

    val res = arr.reduce((a,b) => a-b)
    res:-13

    reduceRight:+

    val res = arr.reduceRight((a,b) => a+b)  过程如下:
    a  b
    -------
    4  5
    3  9
    2  12
    1  14
    res: 15

    reduceRight:-

    val res = arr.reduceRight(_-_)  过程如下:
    a  b
    -------
    4  5
    3  -1
    2  4
    1  -2
    res: 3
    渐变 --> 突变
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  • 原文地址:https://www.cnblogs.com/lybpy/p/9739954.html
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