Question

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
}

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

Answer 1

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
}

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

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