Simple Trigram comparison for 2 strings

trigrams.rb

class Trigrams
  def self.trigramify(str)
    trigs = []
    str.chars.each_cons(3) { |v| trigs << v.join }
    trigs
  end

  def self.match_ratio(str_1, str_2)
    text1_trigs = trigramify(str_1)
    text2_trigs = trigramify(str_2)
    all_cnt = (text1_trigs | text2_trigs).size
    same_cnt = (text1_trigs & text2_trigs).size
    same_cnt.to_f / all_cnt
  end

  def self.compare(str_1, str_2, min_ratio = 0.4)
    match_ratio(str_1, str_2) >= min_ratio
  end
end