Scala for / yield语法 [英] Scala for/yield syntax

问题描述

在我正在学习的书中有一个练习：

编写一个循环来交换整数数组的相邻元素。例如 Array（1,2,3,4,5）变成 Array（2,1,4,3,5）。我的解决方案是：

  var v = Array（0,1,2,3,4 （i < -  0，直到v.length为2）（
 var temp = 0 
 temp = v（i + 1） ; v（i + 1）= v（i）; v（i）= temp 
} 
  

这个算法可以正常工作，利用Scala的潜力，就像我用C ++写的一样。实际上，下面的练习要求：

重复前面的赋值，但是生成一个新的数组。使用 for / yield 。

现在我尝试了：

  val a = ArrayBuffer（1,2,3,4,5）
 var res = for（i < -  0，直到a.length减去2）得到一个（i）$ b $ （i <-1直到a.length减去2）res（i-1）= a（i）<--------- eclipse给我一个错误
  

错误是：值更新不是scala.collection.immutable.IndexedSeq [Int]的成员

我该如何解决这个问题？我知道for / yield的语法是非常强大的，但是我不知道如何使用它。 解决方案

有一个滑动函数可以完全满足您的需求：

 （ for {
i<  -  Array（1,2,3,4,5）.sliding（2,2）
j<  -  i.reverse 
} yield j）.toArray 
  

In the book that I'm studying there is an exercise:

Write a loop that swaps adjacent elements of an array of integer. For example Array(1,2,3,4,5) becomes Array(2,1,4,3,5). My solution is:

var v = Array(0,1,2,3,4,5,6,7,8,9)
for (i <- 0 until v.length by 2) {
  var temp = 0
  temp = v(i+1); v(i+1) = v(i); v(i) = temp
}

This algorithm works fine but isn't written fully exploiting the potential of Scala, it is written as if I wrote in C++. In fact, the following exercise asks:

Repeat the preceding assignment, but produce a new array with the swapped values. Use for/yield.

Now I tried with:

val a = ArrayBuffer(1,2,3,4,5)
var res = for (i <- 0 until a.length by 2) yield a(i)
for (i <- 1 until a.length by 2) res(i-1)=a(i) <---------eclipse give me an error

The error is: "value update is not a member of scala.collection.immutable.IndexedSeq[Int]"

How can I solve this task? I understand that the syntax "for / yield" is very powerful, but I don't know how to use it.

解决方案

There is a sliding function that does exactly what you need:

(for {
  i <- Array(1,2,3,4,5).sliding(2,2)
  j <- i.reverse
} yield j).toArray

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