CODEWITHSUNDEEP
f#
John John
John John

Reputation: 377

F# compare arrays of tuples and return the different elements and index

#light

let a1 = [| (1, 1); (2, 1); (3, 1) |]

let a2 = [| (1, 1); (2, 3); (3, 1) |]

let aa = Array.zip a1 a2
       |> Array.filter(fun (x, y) -> x <> y)

I want to write a function to do this: it will return the different tuple from two arrays, but I also want to return the index of the different tuple in the second array and the corresponding tuple in the second array. (My code did not work totally yet!) For my above example, I want to return: 1 and (2, 3) Another example:

let a1 = [| (1, 1); (2, 1); (3, 1); (4, 1) |]

let a2 = [| (1, 1); (2, 3); (3, 1); (4, 2) |]

I want to return: 1 and (2, 3); 3 and (4, 2) If you have any idea, please show me your code. Besides, I am not used to the new place for F#, the format makes me feel difficult to find a good place to post my questions, therefore, I still post my question here.

Upvotes: 0

Views: 1070

Answers (3)

BLUEPIXY
BLUEPIXY

Reputation: 40145

let diff (a:(int * int)[]) b =
  b
  |> Array.mapi (fun i tp -> if a.[i] <> tp then (i, tp) else (-1, tp))
  |> Array.filter (fun (x, _) -> x >= 0)

DEMO

 > diff a1 a2;;
val it : (int * (int * int)) [] = [|1, (2, 3)); (3, (4, 2))|]

Upvotes: 0

Daniel
Daniel

Reputation: 47904

Here's one way to do it:

let diff a b =
  let s = Set.ofSeq a
  b 
  |> Seq.mapi (fun i x -> i, x)
  |> Seq.filter (fun (_, x) -> not (Set.contains x s))

Example

let a1 = [| (1, 1); (2, 1); (3, 1) |]
let a2 = [| (1, 1); (2, 3); (3, 1) |]
diff a1 a2 //output: seq [(1, (2, 3))]

This works for any collection (list, array, seq<_>, set, etc) and the sequences may be of different lengths. If you know you'll always be using arrays of equal length, you can optimize accordingly (see desco's answer).

Upvotes: 0

desco
desco

Reputation: 16782

let a1 = [| (1, 1); (2, 1); (3, 1) |]

let a2 = [| (1, 1); (2, 3); (3, 1) |]

let diff = 
    (a1, a2) 
    ||> Array.mapi2(fun i t1 t2 -> (i, t1, t2))
    |> Array.choose(fun (i, a, b) -> if a <> b then Some (i, b) else None)

Upvotes: 4

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