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Need a mutable container
f#

Dear All:
I need a mutable container to hold some items.

let beginArray = [| "A"; "B"; "C" |]
let toAddArray = [| "B"; "D"; "E" |]

What I need is to test each element in toAddArray, if already in beginArray, then skip it, if not already in the beginArray, then add it, until all the elements in toAddArray is checked.
So, the result for the above example is:
let endArray = [| "A"; "B"; "C"; "D"; "E" |]

I need a mutable container "endArray", but it is not easy for me to find one.
Please offer your code.
Thanks,

.

If you really need a mutable array you could use type ResizeArray<'T>.

Otherwise you coud use this:

let endArray = Set.toArray(Set.ofArray beginArray + Set.ofArray toAddArray)

or in more F# idiomatic style:

let endArray = set beginArray + set toAddArray |> Set.toArray

By on 10/30/2010 3:27 PM ()

Thanks for your code.
But the code is not what I want.
Since I have to test each element in toAddArray to see if such element is already in beginArray.
Your code simply skip the testing, even it gives the correct result, but I also need the testing, which is important in my programming.
But thanks anyway.

By on 10/31/2010 12:53 AM ()

Hi,

you don't need a mutable container to achieve the result that you want because the Array module in F# gives you the adequate functionality, i think this code solves your problem (sorry for the indentation):

let beginArray = [| "A"; "B"; "C" |]

let toAddArray = [| "B"; "D"; "E" |]

let endArray =

let arr =

[|

for x in toAddArray do

let exist = beginArray |> Array.tryFind (fun y -> y = x)

match exist with

| None -> yield x

| Some _ -> ()

|]

Array.concat [beginArray; arr]

Regards, Taha.

By on 10/31/2010 4:35 AM ()

Hi,
Thank you very much for your code.
I did find a way to use ResizeArray, and I think using ResizeArray is better.
I can understand F# prefers immutable data, but my programming needs from time to time mutable data.
Anyway, thanks for all who have offered help.

By on 10/31/2010 8:30 AM ()

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