如何在Scala中打印地图

Question

好吧,这个问题似乎真的很愚蠢,但我的观点是,如果你看一下Scala 2.7.6 API,他们就不推荐使用mappingToString方法了.因此,应该有更优雅的替代方案来打印自定义格式的Map.因为几乎任何目的,在Map中使用mkString的等价方法非常方便.

你们怎么看待它？除println外,打印地图的编码片段是什么？

Answer 1

mappingToString是特定于Map.

使用 Scala2.8 中新的集合框架，可以通过扩展TraversableLikeMap的任何对象来迭代a 。IterableLike

然后应该使用mkstring方法（2.7 for 中已有）。Iterable

请参阅 Jesse 的这篇博客文章“Strings”，了解 2.7 的mkstring()示例：

/*
   Making use of raw strings to create a multi line string
   I add a | at the beginning of each line so that we can line up the quote nicely 
   in source code then later strip it from the string using stripMargin
*/
scala> val quote = """|I  don-t consider myself a pessimist.                                                                                                 
     |                |I think of a pessimist as someone who is waiting for it to rain.
     |                |And I feel soaked to the skin.
     | 
     |                |Leonard Cohen"""
quote: java.lang.String = 
|I don-t consider myself a pessimist. 
                      |I think of a pessimist as someone who is waiting for it to rain.
                      |And I feel soaked to the skin.

                      |Leonard Cohen

// capilize the first character of each line
scala> val capitalized = quote.lines.
     |                         map( _.trim.capitalize).mkString("\n")
capitalized: String = 
|I don-t consider myself a pessimist.
|I think of a pessimist as someone who is waiting for it to rain.
|And I feel soaked to the skin.

|Leonard Cohen

// remove the margin of each line
scala> quote.stripMargin        
res1: String = 
I don-t consider myself a pessimist. 
I think of a pessimist as someone who is waiting for it to rain.
And I feel soaked to the skin.

Leonard Cohen

// this is silly.  I reverse the order of each word but keep the words in order
scala> quote.stripMargin.         
     |       lines.               
     |       map( _.split(" ").   
     |              map(_.reverse).
     |              mkString (" ")).
     |      mkString("\n")
res16: String = 
I t-nod redisnoc flesym a .tsimissep
I kniht fo a tsimissep sa enoemos ohw si gnitiaw rof ti ot .niar
dnA I leef dekaos ot eht .niks

dranoeL nehoC

Answer 2

该mappingToString方法用于更改每对键/值转换为字符串的方式，然后由该toString方法使用。

我认为这很糟糕。一方面，它为原本不可变的数据结构添加了可变性。如果您有特定的打印要求，那么您最好将它们放在另一个类中。