The many phases of Raindrops from Exercism.

1-solution.rb

require 'prime'
module Raindrops
  extend self

  def convert(n)
    primes = n.prime_division.flatten
    if primes.any? { |x| [3,5,7].include?(x) }
      primes.map do |x|
        case x
        when 3 then 'Pling'
        when 5 then 'Plang'
        when 7 then 'Plong'
        else x
        end
      end.select { |x| x.is_a?(String) }.join
    else
      n.to_s
    end
  end
end

2-solution.rb

require 'prime'
module Raindrops
  extend self

  def convert(n)
    primes = n.prime_division.flatten
    if (primes & [3,5,7]).length > 0
      primes.map do |x|
        case x
        when 3 then 'Pling'
        when 5 then 'Plang'
        when 7 then 'Plong'
        end
      end.join
    else
      n.to_s
    end
  end
end

3-solution.rb

require 'prime'
module Raindrops
  extend self

  def convert(n)
    primes = n.prime_division.flatten
    return n.to_s unless (primes & [3,5,7]).length > 0
    primes.map do |x|
      case x
      when 3 then 'Pling'
      when 5 then 'Plang'
      when 7 then 'Plong'
      end
    end.join
  end
end

4-solution.rb

require 'prime'
module Raindrops
  extend self

  def convert(n)
    primes = n.prime_division.flatten
    return n.to_s unless (primes & [3,5,7]).length > 0
    primes.map { |x| { 3 => 'Pling',
                       5 => 'Plang',
                       7 => 'Plong', }[x] }.join
  end

end

5-solution.rb

require 'prime'
module Raindrops
  extend self

  def convert(n)
    primes = n.prime_division.flatten
    return n.to_s unless (primes & [3,5,7]).length > 0
    primes.select { |x| [3,5,7].include?(x) }.map { |x| "Pl#{{3=>'i',5=>'a',7=>'o'}[x]}ng"}.join
  end

end

6-solution.rb

require 'prime'
module Raindrops
  extend self

  def convert(n)
    c = { 3 => 'i' , 5 => 'a' , 7 => 'o'}
    primes = n.prime_division.flatten
    return n.to_s unless (primes & c.keys).length > 0
    primes.select { |x| c.keys.include?(x) }
          .map    { |x| "Pl#{c[x]}ng" }
          .join
  end

end

7-solution.rb

require 'prime'
module Raindrops
  extend self

  def convert(n)
    primes = n.prime_division.flatten
    return n.to_s unless no_simple_primes?(primes)
    primes.select { |x| small_prime?(x) }
          .map    { |x| "Pl#{conversions[x]}ng" }
          .join
  end

  private

  def no_simple_primes?(primes)
    (primes & conversions.keys).length > 0
  end

  def small_prime?(n)
    conversions.keys.include?(n)
  end

  def conversions
    { 3 => 'i' , 5 => 'a' , 7 => 'o'}
  end
end

8-solution.rb

require 'prime'
module Raindrops
  extend self

  def convert(n)
    return n.to_s unless no_simple_primes?(primes(n))
    primes(n).select(&method(:small_prime?)).map(&method(:pl_ng)).join
  end

  private

  def primes(n)
    n.prime_division.flatten
  end

  def no_simple_primes?(primes)
    (primes & conversions.keys).length > 0
  end

  def small_prime?(n)
    conversions.keys.include?(n)
  end

  def pl_ng(n)
    "Pl#{conversions[n]}ng"
  end

  def conversions
    { 3 => 'i' , 5 => 'a' , 7 => 'o'}
  end
end