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Trigroup
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module Trigroup open NUnit.Framework open FsUnit (* trigroup [1, 2, 3, 4, 5, 6] => [[nil, 1, 2], [1, 2, 3], [2, 3, 4], [3, 4, 5], [4, 5, 6], [5, 6, nil]] trigroup [9, 8, 7, 6] => [[nil, 9, 8], [9, 8, 7], [8, 7, 6], [7, 6, nil]] ถ้าภาษาไหนไม่มี nil/null (มีป่าวหว่า?) เอาแบบด้านล่างนี้ อันไหนก็ได้ *) (* need f# 4.0 [<Test>] let Trigroup() = let drop n ls = None :: (ls |> List.map (fun x -> Some(x))) @ [None] |> List.skip n |> List.take (List.length ls) let tg ls = List.zip3 (drop 0 ls) (drop 1 ls) (drop 2 ls) |> List.map (fun (x,y,z) -> [ x;y;z ] |> List.filter (fun x -> x <> None) |> List.map Option.get) [1;2;3;4;5;6] |> tg |> should equal [[1;2;]; [1;2;3]; [2;3;4]; [3;4;5]; [4;5;6]; [5;6]] [9;8;7;6] |> tg |> should equal [[9;8]; [9; 8; 7]; [8; 7; 6]; [7; 6]] *)
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