Scala 如何访问和更新地图的可变地图中的值

我有一个三级数据结构（缩进和换行以提高可读性）：

访问最里面的数据（分数）需要大量键入：

import org.scalatest.{Assertions, FunSuite}

class MapExamplesSO extends FunSuite with Assertions {
  test("Update values in a mutable map of map of maps") {
    import scala.collection.mutable.Map
    // The m map is essentially an accumulator
    val m = Map("normal" -> 
                Map("home" -> Map("wins" -> 0, "scores" -> 0),
                    "away" -> Map("wins" -> 0, "scores" -> 0)
                  )
          )
    //
    // Is there a less verbose way to increment the scores ?
    //
    assert(m("normal").apply("home").apply("scores") === 0)

    val s1 = m("normal").apply("home").apply("scores") + 1
    m("normal").apply("home").update("scores", s1)

    assert(m("normal").apply("home").apply("scores") === 1)

    val s2 = m("normal").apply("home").apply("scores") + 2
    m("normal").apply("home").update("scores", s2)

    assert(m("normal").apply("home").apply("scores") === 3)
  }
}

是否有一种不那么冗长的方法来修改分数的值

我是一名Scala新手，因此对上述代码的所有其他观察也都是受欢迎的。

您不必使用“apply”，只需使用“（）”正常执行即可

你可以写

m("normal").apply("home").apply("scores")

作为

---

然而，我不确定这样的结构是否是一个好主意。也许你应该考虑把这个功能封装在一个专门的类中。

添加一个本地助手函数总是减少代码复制的好方法：

class MapExamplesSO {
  def test {
    import scala.collection.mutable.Map
    // The m map is essentially an accumulator
    var m = Map("normal" -> 
                Map("home" -> Map("wins" -> 0, "scores" -> 0),
                    "away" -> Map("wins" -> 0, "scores" -> 0)))


    //Local Helper returns (Old, New)
    def updateScore(k1 : String,k2 : String,k3 : String)
                   (f : Int => Int) : (Int, Int) = {
      val old = m(k1)(k2)(k3)
      m(k1)(k2)(k3) = f(old)
      (old, m(k1)(k2)(k3))
    }

    assert(m("normal")(home")("scores") === 0)
    assert(updateScore("normal","home","scores")(_+1)._2 === 1)
    assert(updateScore("normal","home","scores")(_+2)._2 === 3)
  }
}

[编辑使代码更紧凑]

更不冗长：

assert(m("normal")("home")("scores") === 0)

val s1 = m("normal")("home")("scores") + 1
m("normal")("home")("scores") = s1

assert(m("normal")("home")("scores") === 1)

val s2 = m("normal")("home")("scores") + 2
m("normal")("home")("scores") = s2

assert(m("normal")("home")("scores") === 3)

这充分利用了

apply

和

update

都具有如上所示的语法优势。更简短的是：

// On REPL, put both these definitions inside an object instead
// of entering them on different lines
def scores = m("normal")("home")("scores")
def scores_=(n: Int) = m("normal")("home")("scores") = n

assert(scores === 0)

val s1 = scores + 1
scores = s1

assert(scores === 1)

val s2 = scores + 2
scores = s2

// Just so you see these updates are being made to the map:
assert(m("normal")("home")("scores") === 3)

它利用了getter和setter的语法优势

---

（getter定义必须存在，setter定义才能工作）。

聪明！（我只是希望不要太聪明：）在我意识到这里发生了什么之前，我读了几本书。回答得很好，谢谢！这也是一个非常有用的答案-谢谢！我也希望你投更多的票。Getter/setter为初学者解释说：在本例中，这是可行的，但如果m（“normal”）（“home”）尚未定义，则将不起作用。

class MapExamplesSO {
  def test {
    import scala.collection.mutable.Map
    // The m map is essentially an accumulator
    var m = Map("normal" -> 
                Map("home" -> Map("wins" -> 0, "scores" -> 0),
                    "away" -> Map("wins" -> 0, "scores" -> 0)))


    //Local Helper returns (Old, New)
    def updateScore(k1 : String,k2 : String,k3 : String)
                   (f : Int => Int) : (Int, Int) = {
      val old = m(k1)(k2)(k3)
      m(k1)(k2)(k3) = f(old)
      (old, m(k1)(k2)(k3))
    }

    assert(m("normal")(home")("scores") === 0)
    assert(updateScore("normal","home","scores")(_+1)._2 === 1)
    assert(updateScore("normal","home","scores")(_+2)._2 === 3)
  }
}

assert(m("normal")("home")("scores") === 0)

val s1 = m("normal")("home")("scores") + 1
m("normal")("home")("scores") = s1

assert(m("normal")("home")("scores") === 1)

val s2 = m("normal")("home")("scores") + 2
m("normal")("home")("scores") = s2

assert(m("normal")("home")("scores") === 3)

// On REPL, put both these definitions inside an object instead
// of entering them on different lines
def scores = m("normal")("home")("scores")
def scores_=(n: Int) = m("normal")("home")("scores") = n

assert(scores === 0)

val s1 = scores + 1
scores = s1

assert(scores === 1)

val s2 = scores + 2
scores = s2

// Just so you see these updates are being made to the map:
assert(m("normal")("home")("scores") === 3)