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Map by pairs - how to?
f#

Hi all!

I wanna apply some short function to array, that gives me map of all neighbour-pairs or elements.

equivalent to this:

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let map_by_pair (arr: a'[]) f =

    let res = Array.create arr.Length-1

    for idx in [0..arr.Length-1] do

        res.[idx] (left array) f arr.[idx] arr.[idx+1]

    res

for example, if I have array of points, to get the array of segments of all neightbour-pairs.

.

Hi!

You could rewrite the function like this:

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let data = [|1;2;3;4;5|]

let map_by_pair arr f =
   arr
   |> Seq.pairwise
   |> Seq.map (fun (a,b) -> f a b)
   |> Seq.toArray
   
printfn "%A" (map_by_pair data (*))

However, I think there is nothing wrong with your original code. It might very well be faster.

Of course, you might also just use Seq.pairwise directly if it matches the situation.

By on 5/20/2011 10:43 AM ()

Yes, the [b]Seq.pairwise[/b] is the key to.

Thank you a lot and best wishes!

By on 5/20/2011 10:30 PM ()

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