A method to count the frequency that each value within a string of comma separated values appears in another string of comma separated values. Usage: count_frequency_of_string_values(["1,2,"], ["1,2,2,2"]) => ["1-1", "2-3"]

count_frequency_of_string_values.rb

require 'benchmark'
require 'test/unit'

def count_frequency_of_string_values(key, observation)
    # convert arguments into arrays for comparison
    key_array = key.split(",").map { |s| s.to_i }
    observation_array = observation.split(",").map { |s| s.to_i }
    # for each key - count how many matches within observation and add result to the output  
    output = []
    key_array.each do |k|
      frequency = 0
      observation_array.each do |o|
        if k == o then frequency += 1
        end
      end
      output << ("#{k}-#{frequency}")
    end
    output
end

class FrequencyTests < Test::Unit::TestCase
    def test_count_frequency_of_string_values_five_inputs_three_observations
      key = "1,2"
      observation = "1,2,2"
      calculated = count_frequency_of_string_values(key, observation)
      assert_equal ["1-1", "2-2"], calculated 
   end
   
   def test_count_frequency_of_string_values_nine_inputs_thirty_observations
     key = "1,2,3,4,5,6,7,8,9"
     observation = "1,2,3,3,4,4,5,5,6,6,6,7,7,7,7,8,8,8,8,8,9,9,9,9,9,9,9,9,9,9"
     calculated = count_frequency_of_string_values(key, observation)
     assert_equal ["1-1", "2-1", "3-2", "4-2", "5-2", "6-3", "7-4", "8-5", "9-10"], calculated
   end   
end