scala中集合的隐式Impl方法
我在scala中集合的隐式Impl方法,scala,implicit,scala-breeze,Scala,Implicit,Scala Breeze,我在SortedMap[Int,Double]上有一个类型别名,我希望有一个隐式的别名,允许我将SortedMap传递给breeze中的一些内置函数,特别是breeze.stats.函数variance和stddev 下面是一个没有隐含含义的工作示例: package com.soquestion import breeze.linalg._ import breeze.stats._ import scala.collection.SortedMap import scala.languag
SortedMap[Int,Double]
上有一个类型别名,我希望有一个隐式的别名,允许我将SortedMap
传递给breeze中的一些内置函数,特别是breeze.stats.
函数variance
和stddev
下面是一个没有隐含含义的工作示例:
package com.soquestion
import breeze.linalg._
import breeze.stats._
import scala.collection.SortedMap
import scala.language.implicitConversions
object proof {
type Series = SortedMap[Int, Double]
def example: Double = {
val s: Series = SortedMap(1 -> 9.0, 2 -> 2.0, 3 -> 5.0, 4 -> 4.0, 5 -> 12.0, 6 -> 7.0, 7 -> 8.0, 8 -> 11.0, 9 -> 9.0, 10 -> 3.0, 11 -> 7.0, 12 -> 4.0, 13 -> 12.0, 14 -> 5.0, 15 -> 4.0, 16 -> 10.0, 17 -> 9.0, 18 -> 6.0, 19 -> 9.0, 20 -> 4.0)
stddev(s.values)
}
}
在sbt控制台中运行
scala> com.soquestion.proof.example
res0: Double = 3.0607876523260447
我希望不必指定.values
,只需调用stddev
和方差即可
这是我试过的
package com.soquestion
import breeze.linalg._
import breeze.stats._
import scala.collection.SortedMap
import scala.language.implicitConversions
object proof {
// Implicitly convert the SortedMap, or any map, to a DenseVector[Double]
implicit def series2DenseVector(s: Traversable[(Int, Double)]): DenseVector[Double] = {
DenseVector(s.map(_._2).toArray)
}
type Series = SortedMap[Int, Double]
def example: Double = {
val s: Series = SortedMap(1 -> 9.0, 2 -> 2.0, 3 -> 5.0, 4 -> 4.0, 5 -> 12.0, 6 -> 7.0, 7 -> 8.0, 8 -> 11.0, 9 -> 9.0, 10 -> 3.0, 11 -> 7.0, 12 -> 4.0, 13 -> 12.0, 14 -> 5.0, 15 -> 4.0, 16 -> 10.0, 17 -> 9.0, 18 -> 6.0, 19 -> 9.0, 20 -> 4.0)
stddev(s) // <--- compiler error here
}
}
浏览breeze文档时,我没有找到一个好的例子来说明我需要提供什么。理想情况下,我希望创建一个隐式,允许我调用stdev
和variance
,而无需多个隐式
我确实看到了这个问题,但我不知道它将如何应用到这个场景中
基于下面@dlwh答案的完整格式答案,以防将来有人需要它
package com.soquestion
import breeze.linalg.support._
import breeze.linalg.support.CanTraverseValues._
import breeze.stats._
import scala.annotation.tailrec
import scala.collection.SortedMap
import scala.language.implicitConversions
object proof {
type Series = SortedMap[Int, Double]
def example: Double = {
// ideally this implicit would go in a scope higher up so it could be
// brought in wherever it's needed, but this works for a sample
implicit object SeriesIter extends CanTraverseValues[Series, Double] {
def isTraversableAgain(from: Series) = true
def traverse(from: Series, fn: ValuesVisitor[Double]): Unit = {
@tailrec def traverser(idx: Int, t: Array[Double]): Unit = {
if (idx == 1) fn.visit(t.head)
else {
fn.visit(t.head)
traverser(idx - 1, t.tail)
}
}
val v: Array[Double] = from.values.toArray
fn.zeros(0, 0d)
traverser(v.size, v)
}
}
val s: Series = SortedMap(1 -> 9.0, 2 -> 2.0, 3 -> 5.0, 4 -> 4.0, 5 -> 12.0, 6 -> 7.0, 7 -> 8.0, 8 -> 11.0, 9 -> 9.0, 10 -> 3.0, 11 -> 7.0, 12 -> 4.0, 13 -> 12.0, 14 -> 5.0, 15 -> 4.0, 16 -> 10.0, 17 -> 9.0, 18 -> 6.0, 19 -> 9.0, 20 -> 4.0)
stddev(s)
}
}
文档可以做得更好,我真希望我能让错误消息更有帮助
如果你看一下,你会发现它需要一个variance.Impl
的实现,它需要一个meansandvariance.Impl
,它可以为任何具有CanTraverseValues[T,Double]
隐式的类型提供。默认情况下,对于集合有一个隐式的CanTraverseValues
,但仅在包含的类型上,而不是scala的Map
类型的值上。
实现CanTraverseValues和CanMapValues将启用大多数breeze UFUNC
Scala通常不会隐式地“链接”,这就是为什么您的证明示例不起作用的原因。谢谢!我最后添加了以下内容,它很好地解决了隐式对象mapLikeIter扩展CanTraverseValues[Series,Double]{def-isTraversableAgain(from:Series)=true-def-traverse(from:Series,fn:ValuesVisitor[Double]):Unit={@tailrec def-traverser(idx:Int,t:Array[Double]):Unit={if(idx==1)fn.visit(t.head)else{fn.visit(t.head)traverser(idx-1,t.tail)}val v:Array[Double]=from.values.toArray fn.zeros(0,0d)traverser(v.size,v)}为更简单的实现提出了一个更改(实际上没有仔细检查,但我认为它是正确的)
package com.soquestion
import breeze.linalg.support._
import breeze.linalg.support.CanTraverseValues._
import breeze.stats._
import scala.annotation.tailrec
import scala.collection.SortedMap
import scala.language.implicitConversions
object proof {
type Series = SortedMap[Int, Double]
def example: Double = {
// ideally this implicit would go in a scope higher up so it could be
// brought in wherever it's needed, but this works for a sample
implicit object SeriesIter extends CanTraverseValues[Series, Double] {
def isTraversableAgain(from: Series) = true
def traverse(from: Series, fn: ValuesVisitor[Double]): Unit = {
@tailrec def traverser(idx: Int, t: Array[Double]): Unit = {
if (idx == 1) fn.visit(t.head)
else {
fn.visit(t.head)
traverser(idx - 1, t.tail)
}
}
val v: Array[Double] = from.values.toArray
fn.zeros(0, 0d)
traverser(v.size, v)
}
}
val s: Series = SortedMap(1 -> 9.0, 2 -> 2.0, 3 -> 5.0, 4 -> 4.0, 5 -> 12.0, 6 -> 7.0, 7 -> 8.0, 8 -> 11.0, 9 -> 9.0, 10 -> 3.0, 11 -> 7.0, 12 -> 4.0, 13 -> 12.0, 14 -> 5.0, 15 -> 4.0, 16 -> 10.0, 17 -> 9.0, 18 -> 6.0, 19 -> 9.0, 20 -> 4.0)
stddev(s)
}
}