# darraghenright's solution

## to Nucleotide Count in the Elixir Track

Published at Apr 05 2020 · 0 comments
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...

## Running tests

Execute the tests with:

\$ mix test

### 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

If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.

## 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

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

### test_helper.exs

ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)
defmodule NucleotideCount do
@nucleotides [?A, ?C, ?G, ?T]

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

## Examples

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

iex> NucleotideCount.count('AATAA', ?T)
1
"""
@spec count(charlist(), char()) :: non_neg_integer()
def count(strand, nucleotide) do
strand |> Enum.count(&(&1 == nucleotide))
end

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

## Examples

iex> NucleotideCount.histogram('AATAA')
%{?A => 4, ?T => 1, ?C => 0, ?G => 0}
"""
@spec histogram(charlist()) :: map()
def histogram(strand) do
buckets = @nucleotides |> Enum.into(%{}, &{&1, 0})
increment = &(&1 + 1)

strand |> Enum.reduce(buckets, &Map.update(&2, &1, 1, increment))
end
end