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to Nucleotide Count in the Elm Track

Published at Apr 19 2021 · 0 comments
Test suite

Given a single stranded DNA string, compute how many times each nucleotide occurs in the string.

The genetic language of every living thing on the planet is DNA. DNA is a large molecule that is built from an extremely long sequence of individual elements called nucleotides. 4 types exist in DNA and these differ only slightly and can be represented as the following symbols: 'A' for adenine, 'C' for cytosine, 'G' for guanine, and 'T' thymine.

Here is an analogy:

  • twigs are to birds nests as
  • nucleotides are to DNA as
  • legos are to lego houses as
  • words are to sentences as...

Elm Installation

Refer to the Installing Elm page for information about installing elm.

Writing the Code

The code you have to write is located inside the src/ directory of the exercise. Elm automatically installs packages dependencies the first time you run the tests so we can start by running the tests from the exercise directory with:

$ elm-test

To automatically run tests again when you save changes:

$ elm-test --watch

As you work your way through the tests suite in the file tests/Tests.elm, be sure to remove the skip <| calls from each test until you get them all passing!


The Calculating DNA Nucleotides_problem at Rosalind http://rosalind.info/problems/dna/

Submitting Incomplete Solutions

It is possible to submit an incomplete solution so you can see how others have completed the exercise.


module Tests exposing (tests)

import Expect
import NucleotideCount exposing (nucleotideCounts)
import Test exposing (..)

tests : Test
tests =
    describe "NucleotideCount"
        [ test "empty dna strand has no nucleotides" <|
            \() ->
                Expect.equal { a = 0, t = 0, c = 0, g = 0 }
                    (nucleotideCounts "")
        , skip <|
            test "repetitive sequence has only guanine" <|
                \() ->
                    Expect.equal { a = 0, t = 0, c = 0, g = 8 }
                        (nucleotideCounts "GGGGGGGG")
        , skip <|
            test "counts all nucleotides" <|
                \() ->
                    Expect.equal { a = 20, t = 21, c = 12, g = 17 }
module NucleotideCount exposing (nucleotideCounts)

import Task exposing (sequence)

type alias NucleotideCounts =
    { a : Int
    , t : Int
    , c : Int
    , g : Int

nucleotideCounts : String -> NucleotideCounts
nucleotideCounts sequence =
        chars =
            sequence |> String.toList
    { a = count 'A' chars
    , t = count 'T' chars
    , g = count 'G' chars
    , c = count 'C' chars

count : Char -> List Char -> Int
count char chars =
        (\c ->
            if char == c then

        |> List.sum

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