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  1. Practice
  2. Functional Programming
  3. Introduction
  4. Filter Array
  5. Discussions

Filter Array

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votes

  • PitrDubovich + 0 comments

    In Scala, assuming we're not able to use filter, we could instead use the fact that flatMap will filter out values of None.

    arr.flatMap(a => if (a < delim) Some(a) else None)

  • m0smith + 0 comments

    Another Clojure solution. Not lazy unfortunately.

    (fn[delim lst] (reduce #(if (< %2 delim) (conj %1 %2) %1) [] lst))

  • LW
    nevertiree + 1 comment

    Haskell

    f n arr = filter (< n) arr
    • HK
      har33sh + 0 comments

      f n arr = [ a | a <- arr , a < n ]

  • JCrazafy + 1 comment

    I am not particularly convinced that the specifications are tested fully. I used list comprehension to circumvent the use of "filter" and it worked.

    • abhiranjan + 0 comments

      Hi @JCrazafy, thanks for pointing. I have reworded the constraint. It is suggested to write own implementation, not enforced.

  • Darshit_Shah + 0 comments

    Another solution approach in Scala using for expression:

    for (i <- arr if i < delim) yield i

  • Technical_Rambo + 0 comments

    Scala : Create Either Single-Element List Or Empty List for each element based on condition and flatMap to merge them. 

    def f(delim:Int,arr:List[Int]):List[Int] = arr.flatMap(x=>if (x<delim) List(x) else List())

  • MM
    meincke911 + 0 comments

    An F# solution

    open System

[<EntryPoint>]
let main args =
    let x = Console.ReadLine() |> int
    
    let numbers =
        Seq.initInfinite (fun _ -> Console.ReadLine())
        |> Seq.takeWhile (String.IsNullOrWhiteSpace >> not)
        |> Seq.filter (fun v -> v |> int < x)
        |> Seq.iter (printf "%s\n")
    
    0

  • metaculus + 0 comments

    Here is how to read the stdin for this question in Ocaml:

    let f n arr = 
    (* implementation *)
    
let () =
    (* first line is parsed as the first arg to f *)
    let num = int_of_string (read_line ()) in
    
    (* the rest until EOF are parsed into an array for second arg *)
    f num (
        let rec aux arr =
            try
                let input = read_line () in
                    match input with
                    | "" -> arr
                    | a  -> aux (arr @ [int_of_string a])
            with End_of_file -> arr
        in aux [] )

  • R
    ravi_andrew_baj1 + 1 comment

    Any Lisp or Racket solutions?

    • meriororen + 0 comments

      This? Input thanks to @abhiranjan

      (define (read-threshold)
  (let ([x (read)]) x))

(define (read-list)
  (let ([x (read)])
    (if (eof-object? x)
        (list)
        (cons x (read-list)))))
      
(let ([t (read-threshold)]
      [l (read-list)])
  (for ([x l])
       (if (< x t)
           (printf "~a\n" x)
           #f)))

  • csixteen + 0 comments

    Probably not the best Erlang code:

    -module(solution).
-export([main/0, read_input/1]).

read_input(X) ->
	case io:fread("", "~d") of
		eof -> ok;
		{ok, [N]} ->
			if N < X -> io:format("~p~n", [N]);
				N >= X -> ok
			end,
			read_input(X)
	end.

main() ->
	{ok,[X]} = io:fread("", "~d"),
	read_input(X).
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