How to use instance subscript in Swift Tabular Data to access DataFrame Column as an Array

I am attempting to turn a Swift TabularData DataFrame column into an array. The Apple Developer Documentation here describes the following Instance Subscript that does exactly that:

subscript<T>(columnName: String, type: T.Type = T.self) -> [T?] { get set }

However, when I attempt to the following code on a DataFrame (named elevationsDf) with a column (named "PLoss"), it returns a Column<Double> instead of a [Double].

print(type(of: elevationsDf["PLoss", Double.self]))

What should I change to address this issue?

>Solution :

Well, DataFrame also has this subscript:

subscript<T>(columnName: String, type: T.Type) -> Column<T> { get set }

And that is what your code resolves to.

To call the subscript that you want, you can specify the type of the result explicitly:

let c: [Int?] = df["a", Int.self]

Or just:

let c: [Int?] = df["a"]