shmibs's solution to Nucleotide Count on the Elixir track

Instructions

Test suite

Solution

Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

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...

Running tests

Execute the tests with:

$ elixir nucleotide_count_test.exs

Pending tests

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by commenting out the relevant @tag :pending with a # symbol.

For example:

# @tag :pending
test "shouting" do
  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end

Or, you can enable all the tests by commenting out the ExUnit.configure line in the test suite.

# ExUnit.configure exclude: :pending, trace: true

For more detailed information about the Elixir track, please see the help page.

Source

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

Submitting Incomplete Solutions

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

nucleotide_count_test.exs

if !System.get_env("EXERCISM_TEST_EXAMPLES") do
  Code.load_file("nucleotide_count.exs", __DIR__)
end

ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)

defmodule NucleotideCountTest do
  use ExUnit.Case

  # @tag :pending
  test "empty dna string has no adenine" do
    assert NucleotideCount.count('', ?A) == 0
  end

  @tag :pending
  test "repetitive cytosine gets counted" do
    assert NucleotideCount.count('CCCCC', ?C) == 5
  end

  @tag :pending
  test "counts only thymine" do
    assert NucleotideCount.count('GGGGGTAACCCGG', ?T) == 1
  end

  @tag :pending
  test "empty dna string has no nucleotides" do
    expected = %{?A => 0, ?T => 0, ?C => 0, ?G => 0}
    assert NucleotideCount.histogram('') == expected
  end

  @tag :pending
  test "repetitive sequence has only guanine" do
    expected = %{?A => 0, ?T => 0, ?C => 0, ?G => 8}
    assert NucleotideCount.histogram('GGGGGGGG') == expected
  end

  @tag :pending
  test "counts all nucleotides" do
    s = 'AGCTTTTCATTCTGACTGCAACGGGCAATATGTCTCTGTGTGGATTAAAAAAAGAGTGTCTGATAGCAGC'
    expected = %{?A => 20, ?T => 21, ?C => 12, ?G => 17}
    assert NucleotideCount.histogram(s) == expected
  end
end

defmodule DNA do
  @nucleotides [?A, ?C, ?G, ?T]

  @doc """
  Counts individual nucleotides in a DNA strand.

  ## Examples

  iex> DNA.count('AATAA', ?A)
  4

  iex> DNA.count('AATAA', ?T)
  1
  """
  @spec count([char], char) :: non_neg_integer
  def count(strand, nucleotide) do
    cond do
      Enum.member?(@nucleotides, nucleotide) == false ->
        raise ArgumentError, message: "invalid nucleotide"
      true ->
        Enum.count strand, &(
          cond do
            Enum.member?(@nucleotides, &1) == false ->
              raise ArgumentError, message: "invalid strand"
            true ->
              &1 == nucleotide
          end
        )
    end
  end


  @doc """
  Returns a summary of counts by nucleotide.

  ## Examples

  iex> DNA.histogram('AATAA')
  %{?A => 4, ?T => 1, ?C => 0, ?G => 0}
  """
  @spec histogram([char]) :: map
  def histogram(strand) do
    @nucleotides
    |> Enum.map(&( {&1, DNA.count(strand, &1)} ))
    |> Map.new()
  end
end

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