在 Scala 中嵌套 for 推导式是一种好的风格吗？

发布于 2024-11-30 18:46:02 字数 650 浏览 0 评论 0原文

我刚刚发现自己编写了一段如下所示的代码：

  def language(frequencies: Array[String], text: Array[String]) = {
    val allText = text.mkString.replace(" ", "")

    val emaps = for {
      fset <- frequencies
      devs = for {
        i <- 'a' to 'z'
        p = fset.indexOf(i) match {
          case -1 => 0d
          case x  => fset.substring(x + 1, x + 3).toDouble / 100 * allText.size
        }
        a = allText.count(i ==)
        dev = math.pow(p - a, 2)
      } yield dev
    } yield devs.sum

    emaps.min
  }

如您所见，值 emaps 是从字符串数组创建的双精度数组。效果很好。我以前从未见过像这样嵌套的 for-comparatives。可以吗还是我应该以某种方式重构？

原文

I just found myself writing a piece of code that looks like this:

  def language(frequencies: Array[String], text: Array[String]) = {
    val allText = text.mkString.replace(" ", "")

    val emaps = for {
      fset <- frequencies
      devs = for {
        i <- 'a' to 'z'
        p = fset.indexOf(i) match {
          case -1 => 0d
          case x  => fset.substring(x + 1, x + 3).toDouble / 100 * allText.size
        }
        a = allText.count(i ==)
        dev = math.pow(p - a, 2)
      } yield dev
    } yield devs.sum

    emaps.min
  }

As you can see, the value emaps is an array of Doubles created from an array of Strings. It works fine. I just haven't seen for-comprehensions nested like this before. Is it OK or should I refactor somehow?

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哭了丶谁疼 2024-12-07 18:46:02

通常，使用 map 和朋友比在 for 构造的循环部分编写长代码块更标准。由于 allText 不依赖于频率，因此您可以在开始时执行一次：（

val lcounts = 'a' to 'z' map {i => i -> allText.count(i==)} toMap
val emaps = frequencies.map { fset =>
  val devs = 'a' to 'z' map { i =>
    val p = fset.indexOf(i) match {
      case -1 => 0d
      case x  => fset.substring(x+1, x+3).toDouble / 100 * allText.size
    }
    math.pow(p - lcounts(i), 2)
  }
  devs.sum
}

另外，您确定要对负值进行平方吗，即 allText.count(i==) 不为零，但 fset.indexOf (i) 是-1？这看起来很奇怪。）

It's generally more standard to use map and friends than to write long blocks of code in the looping part of the for construct. And since allText doesn't depend on the frequencies, you can do that once at the beginning:

val lcounts = 'a' to 'z' map {i => i -> allText.count(i==)} toMap
val emaps = frequencies.map { fset =>
  val devs = 'a' to 'z' map { i =>
    val p = fset.indexOf(i) match {
      case -1 => 0d
      case x  => fset.substring(x+1, x+3).toDouble / 100 * allText.size
    }
    math.pow(p - lcounts(i), 2)
  }
  devs.sum
}

(Also, are you sure you want to square negative values, i.e. where allText.count(i==) is nonzero, but fset.indexOf(i) is -1? That seems strange.)

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