scala 在元组列表上使用 map() 时的详细表示法
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Verbose notation when using map() on Lists of tuples
提问by flend
I like to have my code quite naively readable.
我喜欢让我的代码非常简单易读。
If I set up a simple list of tuples:
如果我设置一个简单的元组列表：
scala> val a = List(6, 8, 10)
a: List[Int] = List(6, 8, 10)
scala> val b = a zipWithIndex
b: List[(Int, Int)] = List((6,0), (8,1), (10,2))
I'd like to map() on the List, but I find the ._1 ._2 syntax a bit hard-to-read:
我想在列表上 map() ，但我发现 ._1 ._2 语法有点难以阅读：
scala> val c = b map ( a => if(a._1 > 8) a._1 else a._2 )
c: List[Int] = List(0, 1, 10)
To 'name' the tuple, I've used:
为了“命名”元组，我使用了：
scala> val c = b map ( { case (num, i) => if(num > 8) num else i } )
c: List[Int] = List(0, 1, 10)
Two questions:
两个问题：
1) Is there a more concise way to name the tuple members?
1）有没有更简洁的方法来命名元组成员？
2) Is there a considerable performance hit for my version above (it is used in moderately performance-critical code).
2）我上面的版本是否有相当大的性能损失（它用于中等性能关键代码）。
Thanks.
谢谢。
采纳答案by Luigi Plinge
b map Function.tupled((num, i) => if(num > 8) num else i)
avoids pattern matching and for-expressions so should be reasonably performant. I'd normally just use caseas you did though.
避免模式匹配和 for 表达式，因此应该具有合理的性能。我通常只是case像你一样使用。
回答by Paolo Falabella
In this case you might find the equivalent for-comprehension syntax more readable, but it's really a matter of taste...
在这种情况下，您可能会发现等效的 for-comprehension 语法更具可读性，但这确实是一个品味问题......
for {(num, i) <- b} yield if(num >8) num else i
FWIW, I've tried benchmarking the map with and without pattern matching and I got pretty much the same execution time.
FWIW，我试过在使用和不使用模式匹配的情况下对地图进行基准测试，我得到的执行时间几乎相同。
Code I've used:
我用过的代码：
object bench extends scala.testing.Benchmark {
var b:List[(Int, Int)] = _
override def setUp {
val a = (1000000 to 2000000).toList
b = a zipWithIndex
}
def run = b map ( a => if(a._1 > 8) a._1 else a._2 )
}
I've also created another application with a bench1object which has only the version of map with the pattern matching instead of the ._1and ._2.
Results on my oldish netbook (scala 2.9.1, xubuntu 11.10):
我还创建了另一个具有bench1对象的应用程序，该对象只有具有模式匹配的 map 版本而不是._1and ._2。我的旧上网本（scala 2.9.1，xubuntu 11.10）上的结果：
$ scala bench 10
bench$ 750 758 731 721 733 736 725 743 735 736
$ scala bench1 10
bench1$ 774 772 740 724 745 730 711 739 740 740
