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All triplets (newbie level)
f#

Hi all!

Please, help me in such simple task:

A have a list of some objects, and needed to create the new list, consist of non-ordered triplets on these objects.

For example, if I have the list of points, and needed to create list of all triangles build on these points as vertices.

(Sorry for language - english isn't my native).

Thank you a lot!

.

If n=3 always, maybe just:

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let list = [(1,2);(2,3);(3,4);(4,5)]
let ans = [for i in list do for j in list do for k in list do if i<>j && j<>k && k<>i then yield [i;j;k]]

val ans : (int * int) list list =

[[(1, 2); (2, 3); (3, 4)]; [(1, 2); (2, 3); (4, 5)];
[(1, 2); (3, 4); (2, 3)]; [(1, 2); (3, 4); (4, 5)];
[(1, 2); (4, 5); (2, 3)]; [(1, 2); (4, 5); (3, 4)];
[(2, 3); (1, 2); (3, 4)]; [(2, 3); (1, 2); (4, 5)];
[(2, 3); (3, 4); (1, 2)]; [(2, 3); (3, 4); (4, 5)];
[(2, 3); (4, 5); (1, 2)]; [(2, 3); (4, 5); (3, 4)];
[(3, 4); (1, 2); (2, 3)]; [(3, 4); (1, 2); (4, 5)];
[(3, 4); (2, 3); (1, 2)]; [(3, 4); (2, 3); (4, 5)];
[(3, 4); (4, 5); (1, 2)]; [(3, 4); (4, 5); (2, 3)];
[(4, 5); (1, 2); (2, 3)]; [(4, 5); (1, 2); (3, 4)];
[(4, 5); (2, 3); (1, 2)]; [(4, 5); (2, 3); (3, 4)];
[(4, 5); (3, 4); (1, 2)]; [(4, 5); (3, 4); (2, 3)]]

Or you could use a permutation fn - but probably overkill.

By on 4/3/2011 11:28 AM ()

Ah, you did say non-ordered - maybe a combinaton fn is better for you - search for "F# combinations", such as:

[link:stackoverflow.com]

By on 4/3/2011 12:02 PM ()

Yes, that's it.

There isn't ready-to-apply solution, but good food for thought. The further I will do myself.

The most likely method is - in fourth (of five) answer.

Thank you a lot!

By on 4/4/2011 8:29 AM ()

Here is my solution, if you interest:

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let cart_filtered (alst: Vector3[]) =
    let seq1 = seq { for i in alst -> [| for j in (alst |> Array.filter (fun x-> x <> i)) -> [|for k in (alst |> Array.filter(fun x -> ((x <> i) && (x <> j)) )) -> (i,j, k) |]|] }

    Array.concat (Array.concat seq1)
By on 4/5/2011 8:17 AM ()

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