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#ruby Counting Vowels

Just saw a simple exercise in my Facebook feed and I thought I give it a shot. The problem is simple:

Write a function that returns the number of vowels in the string.

Here’s my ruby solution:

  require 'minitest/autorun'

  def vowel_count(s)
    vowels = %w[a e i o u]
    s.to_s.scan(/\w/).select { |i| i if vowels.include?(i.downcase) }.count
  end

  describe "#vowel_count" do
    it "should count upcase lowercase" do
      test = "I wanted to be an astronaut"
      vowel_count(test).must_equal 10
    end

    it "should be zero for empty string" do
      vowel_count("").must_equal 0
    end

    it "should be zero for nil" do
      vowel_count(nil).must_equal 0
    end
  end

Sounds simple, right? But there are subtle things you should watch out for.

  • Upper and lower cases may seem trivial but programmers are often bitten by these when comparing strings.
  • An initial solution would be to access each character via [index] and increment a counter for vowels. Here is where familiarity with your language’s libraries becomes useful. While I didn’t get the right method initially, I know Ruby’s String library offers a way to extract regex matches. From then on, it’s just a matter of using Enumerable#select which is a common Ruby idiom for filtering elements.
  • Having tests even for a simple code is a good discipline to have. My initial test only covers the functional requirement. When I added the case of nil it quickly showed the flaw in my code, which brings me to my next point.
  • Produce sensible results as much as possible. While you can argue the requirement states a string and not a nil, it is good habit to defend your code in case the caller passed an invalid value. Hence, I converted the parameter to a string to ensure the rest of the code is working with a string object and it gives a sensible result even if the passed parameter is not a string.

Minimalist testing

If you are working with Rails' for a while, you probably been pampered with Rails seamless integration with testing frameworks you’ll be forgiven if you think these support are only available within Rails.

Ruby comes with minitest/autorun that supports a minimalist testing framework. Just require in your code and you are good to go with rspec-style testing right off the bat.

$ ruby vowelcount.rb
Run options: --seed 47907

# Running:

...

Finished in 0.001155s, 2597.4026 runs/s, 2597.4026 assertions/s.

3 runs, 3 assertions, 0 failures, 0 errors, 0 skips
13 Nov 2014