angelikatyborska's solution to Nucleotide Count on the Ruby track

Instructions

Test suite

Solution

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...

For installation and learning resources, refer to the exercism help page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

gem install minitest

If you would like color output, you can require 'minitest/pride' in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

ruby nucleotide_count_test.rb

To include color from the command line:

ruby -r minitest/pride nucleotide_count_test.rb

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.rb

require 'minitest/autorun'
require_relative 'nucleotide_count'

class NucleotideTest < Minitest::Test
  def test_empty_dna_strand_has_no_adenosine
    assert_equal 0, Nucleotide.from_dna('').count('A')
  end

  def test_repetitive_cytidine_gets_counted
    skip
    assert_equal 5, Nucleotide.from_dna('CCCCC').count('C')
  end

  def test_counts_only_thymidine
    skip
    assert_equal 1, Nucleotide.from_dna('GGGGGTAACCCGG').count('T')
  end

  def test_counts_a_nucleotide_only_once
    skip
    dna = Nucleotide.from_dna('CGATTGGG')
    dna.count('T')
    dna.count('T')
    assert_equal 2, dna.count('T')
  end

  def test_empty_dna_strand_has_no_nucleotides
    skip
    expected = { 'A' => 0, 'T' => 0, 'C' => 0, 'G' => 0 }
    assert_equal expected, Nucleotide.from_dna('').histogram
  end

  def test_repetitive_sequence_has_only_guanosine
    skip
    expected = { 'A' => 0, 'T' => 0, 'C' => 0, 'G' => 8 }
    assert_equal expected, Nucleotide.from_dna('GGGGGGGG').histogram
  end

  def test_counts_all_nucleotides
    skip
    s = 'AGCTTTTCATTCTGACTGCAACGGGCAATATGTCTCTGTGTGGATTAAAAAAAGAGTGTCTGATAGCAGC'
    dna = Nucleotide.from_dna(s)
    expected = { 'A' => 20, 'T' => 21, 'G' => 17, 'C' => 12 }
    assert_equal expected, dna.histogram
  end

  def test_validates_dna
    skip
    assert_raises ArgumentError do
      Nucleotide.from_dna('JOHNNYAPPLESEED')
    end
  end
end

class Nucleotide
  DNA_NUCLEOTIDES = %w(A C G T)
  REGEXP = Regexp.new('\A(' + DNA_NUCLEOTIDES.join('|') + ')*\z')

  def initialize(dna)
    if valid_dna?(dna)
      @dna = dna
    else
      raise ArgumentError, "#{ dna } is not a valid DNA string"
    end
  end

  def self.from_dna(dna)
    new(dna)
  end

  def histogram
    @histogram ||= @dna.chars.each_with_object(empty_histogram) do |nucleotide, histogram|
      histogram[nucleotide] += 1
    end
  end

  def count(nucleotide)
    histogram[nucleotide]
  end

  private

  def valid_dna?(string)
    string =~ REGEXP
  end

  def empty_histogram
    Hash[DNA_NUCLEOTIDES.collect { |nucleotide| [nucleotide, 0] }]
  end
end

Community comments

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angelikatyborska

Solution Author

commented about 5 years ago

My first instinct was to use string.chars.all? { |char| DNA_NUCLEOTIDES.include?(char) }

to validate a DNA string, but I stopped to think about speed. I didn't know if a regular expression would be faster, so I wrote this little benchmark. A regular expression is faster in all the cases I have checked: for valid and for random strings, for a few of really long strings and for many short strings. Sometimes it's 3 times faster, sometimes it's over 100 times faster.

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angelikatyborska's solution

to Nucleotide Count in the Ruby Track

Source

Submitting Incomplete Solutions

nucleotide_count_test.rb

Community comments

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