scala 通过遍历地图构建字符串
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/5985266/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
scala build up string from iterating over map
提问by user747980
if i have a map and want to build up a string from iterating over it, is there a way to have the final string be a result of an expression instead of defining a variable and modifying that inside a loop?
如果我有一张地图并想通过对其进行迭代来构建一个字符串，有没有办法让最终字符串成为表达式的结果，而不是定义一个变量并在循环内修改它？
instead of this
而不是这个
val myMap = Map("1" -> "2", "3"->"4")
var s = ""
myMap foreach s += ...
i'd rather it be
我宁愿它是
var s = myMap something ...
采纳答案by Ben James
You can do this with a fold:
你可以用折叠来做到这一点：
scala> myMap.foldLeft("") { (s: String, pair: (String, String)) =>
| s + pair._1 + pair._2
| }
res0: java.lang.String = 1234
回答by Daniel C. Sobral
I'd just mapand mkString. For example:
我只是map和mkString。例如：
val s = (
Map("1" -> "2", "3"->"4")
map { case (key, value) => "Key: %s\nValue: %s" format (key, value) }
mkString ("", "\n", "\n")
)
回答by Kevin Wright
As for Daniel's answer, but with a couple of optimisations and my own formatting preferences:
至于丹尼尔的回答，但有一些优化和我自己的格式偏好：
val myMap = Map("1" -> "2", "3"->"4")
val s = myMap.view map {
case (key, value) => "Key: " + key + "\nValue: " + value
} mkString ("", "\n", "\n")
The optimisations:
优化：
- By first creating a
viewof the map, I avoid creating an intermediate collection - On profiling, direct String concatenation is faster than
String.format
- 通过首先创建
view地图的一个，我避免创建一个中间集合 - 在分析时，直接字符串连接比
String.format
回答by Diego Sevilla
I'm fairly new to Scala, but you can try reduceLeft. It goes accumulating a partial value (the string being joined with every element). For example, if you want the keys (or the values) joined in a string, just do:
我对 Scala 还很陌生，但你可以试试reduceLeft. 它会累积一个部分值（与每个元素连接的字符串）。例如，如果您希望将键（或值）连接到一个字符串中，只需执行以下操作：
val s = myMap.keys.reduceLeft( (e, s) => e + s)
This results in "13"
这导致“ 13”
回答by Antonin Brettsnajdr
This works also fine if you don't bother about your own formatting:
如果您不担心自己的格式，这也很好用：
scala> Map("1" -> "2", "3"->"4").mkString(", ")
res6: String = 1 -> 2, 3 -> 4
