CODEWITHSUNDEEP
f#
user3507072
user3507072

Reputation: 287

F# list transposition with list list list?

In F#, how would I make the list transposition function compatible with an int list list list ?

let rec transpose = 
   function
    | (_::_)::_ as M -> List.map List.head M :: transpose (List.map List.tail M)
    | _ -> []

It looks like this only works with int list list. However, I have further grouped the inner most list to make int list list list .

Upvotes: 0

Views: 501

Answers (1)

gileCAD
gileCAD

Reputation: 2493

With an int list list list, it depends on which matrices you want to transpose: the inner ones or the outer one or both. In the last case it will depend on the transpositions order.

let rec transpose = function
| (_::_)::_ as M -> List.map List.head M :: transpose (List.map List.tail M)
| _ -> []

// (a (b (c))) -> (a (c (b)))
let transpose0 m = m |> List.map transpose

// (a (b (c))) -> (b (a (c)))
let transpose1 m = m |> transpose

// (a (b (c))) -> (b (c (a)))
let transpose2 m = m |> transpose |> List.map transpose

// (a (b (c))) -> (c (a (b)))  
let transpose3 m = m |> List.map transpose |> transpose

// (a (b (c))) -> (c (b (a)))  
let transpose4 m = m |> transpose |> List.map transpose |> transpose

Upvotes: 2

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