F# function takes too many arguments or used in a context not expected

Question

I'm trying to implement a cost function and I currently have

let computeCost (X : Matrix<double>) (y : Vector<double>) (theta : Vector<double>) =
    let m = y.Count |> double
    let J = (1.0/(2.0*m))*(((X*theta - y) |> Vector.map (fun x -> x*x)).Sum)
    J

For some reason I get an error on the half after the first * saying "This function takes too many arguments, or is used in a context where a function is not expected."

However, when I do this

let computeCost (X : Matrix<double>) (y : Vector<double>) (theta : Vector<double>) =
    let m = y.Count |> double
    let J = (((X*theta - y) |> Vector.map (fun x -> x*x)).Sum)
    J

It works perfectly fine and it says that val J:float which is what I expect. But as soon as add in the second piece which is the (1.0/(2.0*m)) part I get the error. I have parenthesis around everything so I don't see how it can be some partial function being applied or something along those lines. I'm sure it's something dumb but I can't seem to figure it out.

score 0 · Accepted Answer · answered Mar 05 '16 at 03:21

Nevermind, I'm dumb and I fell back into my C# ways of using .Sum() The actual way of using it is

let computeCost (X : Matrix<double>) (y : Vector<double>) (theta : Vector<double>) =
    let m = y.Count |> double
    let J = (1.0/(2.0*m)) * (((X*theta - y) |> Vector.map (fun x -> x*x)) |> Vector.sum)
    J

And this seemed to fix it.

F# function takes too many arguments or used in a context not expected

1 Answers1