F# - Natural Sort Of Strings Containing Numbers - f#

Question

Is there an F# equivalent of Sorting for Humans: Natural Sort Order? For example, reproducing the following example:
Actual (List.sort) : let strngLst = ["1-5"; "10-15"; "15-20"; "5-10"]
Expected : let strngLst = ["1-5"; "5-10"; "10-15"; "15-20"]
Please advise?

Answer 1

Based on the Python 3-liner in that article, I would do something like this:
open System
open System.Text.RegularExpressions
let sortNicely l =
let convert text =
match Int32.TryParse(text) with
| true, i -> Choice1Of2 i
| false, _ -> Choice2Of2 text
let alphanumKey key =
Regex("([0-9]+)").Split(key) |> Array.map convert
List.sortBy alphanumKey l
The main difference is the use of the Choice type. The Python version cleverly uses dynamic typing in convert: Python always considers an int to be less than a string, so convert can return either an int or a string and sort will do what we want. But in F# we need to be more explicit. I used a discriminated union because it does what we want too: a value of the first case (Choice1Of2) is always less than a value of the second case (Choice2Of2).

Answer 2

Based on #matekus' comment, possibly the most correct solution is to port the AlphaNum sort to F#, so:
let len = String.length
let isnum (s: string) i =
let c = s.Chars i
c >= '0' && c <= '9'
let chunk s f t = (f < len s) && (t < len s) && (isnum s f) = (isnum s t)
let chunkto s f =
let rec to_ s f e = if chunk s f e then to_ s f (e + 1) else e in to_ s f f
let int_of_string str =
let v = ref 0
if System.Int32.TryParse(str, v) then !v else 0
let alphanumcmp a b =
let rec chunkcmp a ai b bi =
let al, bl = len a, len b
if ai >= al || bi >= bl then compare al bl else
let ae, be = chunkto a ai, chunkto b bi
let sa, sb = a.Substring(ai, (ae-ai)), b.Substring(bi, (be-bi))
let cmp = if isnum a ai && isnum b bi then compare (int_of_string sa) (int_of_string sb) else compare sa sb
if cmp = 0 then chunkcmp a ae b be else cmp
in chunkcmp a 0 b 0
type AlphanumComparer() =
interface System.Collections.IComparer with
member this.Compare(x, y) =
alphanumcmp (x.ToString()) (y.ToString())
Test:
let names = [ "1000X Radonius Maximus"; "10X Radonius"; "200X Radonius"; "20X Radonius"; "20X Radonius Prime"; "30X Radonius"; "40X Radonius"; "Allegia 50 Clasteron"; "Allegia 500 Clasteron"; "Allegia 51 Clasteron"; "Allegia 51B Clasteron"; "Allegia 52 Clasteron"; "Allegia 60 Clasteron"; "Alpha 100"; "Alpha 2"; "Alpha 200"; "Alpha 2A"; "Alpha 2A-8000"; "Alpha 2A-900"; "Callisto Morphamax"; "Callisto Morphamax 500"; "Callisto Morphamax 5000"; "Callisto Morphamax 600"; "Callisto Morphamax 700"; "Callisto Morphamax 7000"; "Callisto Morphamax 7000 SE";"Callisto Morphamax 7000 SE2"; "QRS-60 Intrinsia Machine"; "QRS-60F Intrinsia Machine"; "QRS-62 Intrinsia Machine"; "QRS-62F Intrinsia Machine"; "Xiph Xlater 10000"; "Xiph Xlater 2000"; "Xiph Xlater 300"; "Xiph Xlater 40"; "Xiph Xlater 5"; "Xiph Xlater 50"; "Xiph Xlater 500"; "Xiph Xlater 5000"; "Xiph Xlater 58" ];;
names |> List.sortWith alphanumcmp |> printf "%A"
Results:
["10X Radonius"; "20X Radonius"; "20X Radonius Prime"; "30X Radonius";
"40X Radonius"; "200X Radonius"; "1000X Radonius Maximus";
"Allegia 50 Clasteron"; "Allegia 51 Clasteron"; "Allegia 51B Clasteron";
"Allegia 52 Clasteron"; "Allegia 60 Clasteron"; "Allegia 500 Clasteron";
"Alpha 2"; "Alpha 2A"; "Alpha 2A-900"; "Alpha 2A-8000"; "Alpha 100";
"Alpha 200"; "Callisto Morphamax"; "Callisto Morphamax 500";
"Callisto Morphamax 600"; "Callisto Morphamax 700"; "Callisto Morphamax 5000";
"Callisto Morphamax 7000"; "Callisto Morphamax 7000 SE";
"Callisto Morphamax 7000 SE2"; "QRS-60 Intrinsia Machine";
"QRS-60F Intrinsia Machine"; "QRS-62 Intrinsia Machine";
"QRS-62F Intrinsia Machine"; "Xiph Xlater 5"; "Xiph Xlater 40";
"Xiph Xlater 50"; "Xiph Xlater 58"; "Xiph Xlater 300"; "Xiph Xlater 500";
"Xiph Xlater 2000"; "Xiph Xlater 5000"; "Xiph Xlater 10000"]val it : unit = ()