Scala: generic weighted average function

Question

I want to implement a generic weighted average function which relaxes the requirement on the values and the weights being of the same type. ie, I want to support sequences o

Answer 1

First of all your template is wrong. (And sorry if the "template" expression is wrong - I am a novice in scala). Your functions expect tuples where both elements are of the same type ( [A: Numeric] ) , instead of tuples where elements are of different types ( [A: Numeric, B: Numeric] ) ( (Int, Float) vs (Float, Float) )

Anyway the below compiles and hopefully will work well after you fill it with your desired calculus.

import scala.collection._

def weightedSum[A: Numeric, B: Numeric](weightedValues: GenSeq[(A,B)]): (A,B) = {
  weightedValues.foldLeft((implicitly[Numeric[A]].zero, implicitly[Numeric[B]].zero)) { (z, t) =>
    (   implicitly[Numeric[A]].plus(z._1, t._1), 
        implicitly[Numeric[B]].plus(z._2, t._2)
    ) 
  } 
}

def weightedAverage[A: Numeric, B: Numeric](weightedValues: GenSeq[(A,B)]): A = {
  val (weightSum, weightedValueSum) = weightedSum(weightedValues)
  implicitly[Numeric[A]] match {
    case num: Fractional[A] => implicitly[Numeric[A]].zero
    case num: Integral[A] => implicitly[Numeric[A]].zero
    case _ => sys.error("Undivisable numeric!")
  }
}

val values1: Seq[(Float, Float)] = List((1, 2f), (1, 3f))
val values2: Seq[(Int, Float)] = List((1, 2f), (1, 3f))

val wa1 = weightedAverage(values1)
val wa2 = weightedAverage(values2)