# paulfioravanti's solution

## to Nucleotide Count in the Elixir Track

Published at Jul 13 2018 · 0 comments
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
``````

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

``````if !System.get_env("EXERCISM_TEST_EXAMPLES") do
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 NucleotideCount do
@nucleotides [?A, ?C, ?G, ?T]

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

## Examples

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

iex> NucleotideCount.count('AATAA', ?T)
1
"""
@spec count([char], char) :: non_neg_integer
def count(strand, nucleotide) do
Enum.reduce(strand, 0, fn char, count ->
case char do
^nucleotide -> count + 1
_ -> count
end
end)
end

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

## Examples

iex> NucleotideCount.histogram('AATAA')
%{?A => 4, ?T => 1, ?C => 0, ?G => 0}
"""
@spec histogram([char]) :: map
def histogram(strand) do
Enum.reduce(strand, initial_nucleotides(), fn char, histogram ->
Map.update(histogram, char, 1, fn value ->
value + 1
end)
end)
end

defp initial_nucleotides do
Enum.reduce(@nucleotides, %{}, fn elem, map ->
Map.put(map, elem, 0)
end)
end
end``````