f# return sorting indices from array.sort

Question

for F# array, is there an easy way to return sorting indices along with the sorted array? like the sort() function from Matlab?

Background: I came from matlab/R, where manipulating array on indices are essential. I'd like to reproduce some index functions and trying to be able to pass indices array around as a variable in various functions. for this sort() function, one usage would be sorting several aligned arrays together based on any one of them. Maybe there are better ways to do this?

Answer 1

Use Array.sort in combination with Array.mapi.

let arr = [| 14;3;11;2 |]
let sortedWithIndex = arr |> Array.mapi (fun x t -> (t,x)) |> Array.sort 
printfn "%A" sortedWithIndex

output

[|(2, 3); (3, 1); (11, 2); (14, 0)|]

Answer 2

let sortWithIndex list =
    list
    |> List.mapi (fun index x -> (x, index))
    |> List.sort

(Depending on the version of F#, List.sort might require a comparison function like `compare ).