提供类型不匹配错误Scala的方法中的调用方法

Question

So I'm trying to call a method("Mean") from inside another method("Centre"), it's giving a type mismatch error.

But if I execute the method("Mean") seperately and store it's result in some variable and then execute method("Centre") using the variable instead of method("Mean"), it works.

Can anyone please explain why?

val X = Vector(3.0,4,5)
val Y = Vector(6,9.0,15)

type D = Double
type V = Vector[D]
def Mean (v:V)= v.sum/v.length
val meanX = Mean(X)
def Centre (v:V) = v.map(X => X - Mean(X))
Centre(X)

Error:

command-1723108043672149:8: error: type mismatch;
found   : D
(which expands to)  Double
required: V
(which expands to)  scala.collection.immutable.Vector[Double]
def Centre (v:V) = v.map(X => X - Mean(X))

but it works if I use "meanX" instead of "Mean(X):

Centre: (v: V)scala.collection.immutable.Vector[Double]
res36: scala.collection.immutable.Vector[Double] = Vector(-1.0, 0.0,1.0)

Answer 1

Mean() is defined to take an argument of type V (ie Vector[Double] ) but in this code, v.map(X => X - Mean(X)) you're trying to pass a Double value instead, because you have redefined the variable X . Thus the error.

I think what you want to do is v.map(n => n - Mean(X)) or, better yet, v.map(_ - Mean(X)) . That way X has only one meaning.