Question

let dTuples = new Dictionary<int, string * string * int>()
dTuples.Add(1, ("A", "OK", 1))
dTuples.Add(2, ("B", "NOK", 2))
dTuples.Add(3, ("C", "OK", 3))

I want to find the items from the dictionary where they have “OK” in the second element of the value part.
I also want to convert the result to an array of tuple without the key part of the dictionary.
For the above example, I need this:

let tuplesOK = [| ("A", "OK", 1); ("C", "OK", 3) |]

If you provide the code, please also add some explanation, so I can understand it better!
Thanks,
John

Answer 1

The solution by Daniel clearly answers your question, but if you need to perform a lookup in the dictionary based on something else than the key, then you may want to consider using a different data structure, because there is no point in using the dictionary. Maybe you could just use a list:

let data =
  [ ("A", "OK", 1)
    ("B", "NOK", 2)
    ("C", "OK", 3) ]

And then perform lookup using Seq.filter just like in the solution by Daniel:

data |> Seq.filter (fun (_, ok, _) -> ok = "OK")
     |> Seq.toArray

Or if you need you’re going to perform the lookup often, you could group the values using the second element (OK/NOK flag) and then store that in a dictionary using the dict function:

// build a dictionary with second element of the tuple as a key 
let lookupOk = data |> Seq.groupBy (fun (_, ok, _) -> ok) |> dict

// get a sequence of 'OK' values
lookupOk.["OK"]