如何在 Scala 中实现通用平均函数? [英] How to implement generic average function in scala?

问题描述

对于任何特定类型的数字，即双精度/整数，这似乎是一个简单的问题，但在一般情况下很难编写.

It seems easy problem for any specific kind of Number i.e. Double/Integer but it is hard to write in general case.

implicit def iterebleWithAvg(data:Iterable[Double]) = new {
    def avg:Double = data.sum / data.size
}

如何为任何类型的 Number(Int,Float,Double,BigDecemial) 实现这个?

How to implement this for any kind of Number(Int,Float,Double,BigDecemial)?

推荐答案

你必须传递一个隐式的Numeric，它允许求和并转换为双精度:

You have to pass an implicit Numeric which will allow summation and conversion to Double:

def average[T]( ts: Iterable[T] )( implicit num: Numeric[T] ) = {
  num.toDouble( ts.sum ) / ts.size
}

编译器会为你提供正确的实例:

The compiler will provide the correct instance for you:

scala> average( List( 1,2,3,4) )
res8: Double = 2.5

scala> average( 0.1 to 1.1 by 0.05 )
res9: Double = 0.6000000000000001

scala> average( Set( BigInt(120), BigInt(1200) ) )
res10: Double = 660.0

您可以使用该函数定义隐式视图(前提是您传播隐式数字依赖项):

You can the use the function to define an implicit view (provided you propagate the implicit numeric dependency):

implicit def iterebleWithAvg[T:Numeric](data:Iterable[T]) = new {
  def avg = average(data)
}

scala> List(1,2,3,4).avg
res13: Double = 2.5

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