如何在Scala中打印地图

Question

好的，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？打印除println以外的地图的编码片段是什么？

Answer 1

mappingToString 方法用于更改每对键/值转换为String的方式，然后由 toString 方法使用。

我觉得这很糟糕。一方面，它为其他不可变数据结构添加了可变性。如果您有特定的打印要求，那么最好将它们放在另一个类中。

Answer 2

mappingToString 特定于 Map 。

使用Scala2.8中的新集合框架， Map 可以被任何 IterableLike 迭代，扩展 TraversableLike 。

方法 mkstring （已经在2.7中为 Iterable ）然后应该使用。

请参阅此博客文章“字符串”作者：Jesse ，2.7 mkstring（）例子：

/*
   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 3

您还可以将 Iterator.map（）与 mkString（）结合使用，例如从 map [String，String]创建查询字符串：

val queryString = updatedMap.map(pair => pair._1+"="+pair._2).mkString("?","&","")