Question

I have written this F# code to count word frequencies in a list and return a tuple to C#. Could you tell me how can I make the code more efficient or shorter?

let rec internal countword2 (tail : string list) wrd ((last : string list), count) =
match tail with
| [] -> last, wrd, count
| h::t -> countword2 t wrd (if h = wrd then last, count+1 else last @ [h], count)

let internal countword1 (str : string list) wrd =
let temp, wrd, count = countword2 str wrd ([], 0) in
temp, wrd, count

let rec public countword (str : string list) =
match str with
| [] -> []
| h::_ ->
  let temp, wrd, count = countword1 str h in
       [(wrd, count)] @ countword temp

Answer 1

If you want to count word frequencies in a string list, your approach seems to be overkill. Seq.groupBy is well-fitted for this purpose:

let public countWords (words: string list) = 
   words |> Seq.groupBy id
         |> Seq.map (fun (word, sq) -> word, Seq.length sq)
         |> Seq.toList