F# program that uses List.sort
let shapes = ["triangle"; "square"; "ellipse"; "rectangle"]
// Use List.sort to sort the string list.
// ... A sorted copy is returned.
let result = List.sort shapes
// Print both lists.
printfn "Unsorted: %A" shapes
printfn " Sorted: %A" result
Output
Unsorted: ["triangle"; "square"; "ellipse"; "rectangle"]
Sorted: ["ellipse"; "rectangle"; "square"; "triangle"]

List.sortBy. This function is more advanced. It lets us select a key to sort for each element. The lambda we pass to sortBy must return a value—this is sorted.

Result: SortBy returns a copy of the List that is sorted. As with sort, the original is not changed.

F# program that uses List.sortBy, sorts strings by length
let values = ["aa"; "x"; "zzz"; "yy"; "eeee"]
// Sort the string list by length in ascending (low to high) order.
let result = List.sortBy (fun (x : string) -> x.Length) values
// Print our results.
List.iter(fun x -> printfn "%A" x) result
Output
"x"
"aa"
"yy"
"zzz"
"eeee"

Array.sort, sortInPlace. An array in F# is not the same as a list—an array is a low-level region of memory with elements. We must use special Array functions to sort.Array

Array.sort: This returns a copied array that is sorted. It does not modify (mutate) the original array's data.

Array.sortInPlace: This rearranges the elements in an existing array. No new memory region is allocated.

Seq.sort, pipeline. We can sort collections with Seq.sort. With Seq.ofList, we treat a list as a sequence. Then we can use functions like where and sort in a pipeline.

Here: We use "where" to only keep elements containing a lowercase "A." Then we sort them alphabetically, and convert back to a list.

F# program that uses Seq.sort
let animals = ["cat"; "bird"; "zebra"; "leopard"; "shark"]
// Act on list as a sequence.
// ... Use where to filter our list.
// Use Seq.sort to sort the sequence.
// Use Seq.toList to convert back to a list.
let sortResult =
Seq.ofList animals
|> Seq.where (fun x-> x.Contains "a")
|> Seq.sort
|> Seq.toList
// Print all our results.
List.iter (fun (x : string) -> printfn "%A" x) sortResult
Output
"cat"
"leopard"
"shark"
"zebra"

With this language, we have features that are well-suited to advanced sorting. We have lambdas and immutable collections (like lists). We invoke built-in sort methods.