Ruby script to check a degree of string similarity by n-gram model

check_string_similarity_by_ngram.rb

#!/usr/local/bin/ruby
# coding: utf-8
#********************************************************************
# Ruby script to check a degree of string similarity by n-gram model.
#********************************************************************
#
class String
  def sim_ngram(str, n = 3)
    # 空白文字(半角スペース、改行、復帰、改ページ、水平タブ)は除去
    strings = [self.gsub(/\s+/, ""), str.gsub(/\s+/, "")]
    lengths = strings.map { |s| s.split(//).size }
    # 文字列の文字数が N より少なければ例外スロー
    raise "Length of a self string is shorter than N(=#{n})"   if lengths[0] < n
    raise "Length of a target string is shorter than N(=#{n})" if lengths[1] < n

    # N 文字ずつ分割
    arrays = strings.map { |s| s.chars.each_cons(n).collect(&:join) }
    # 重複要素数
    count_dup = (arrays[0] & arrays[1]).size
    # 全要素数
    count_all = (arrays[0] + arrays[1]).uniq.size
    # 類似度返却
    return count_dup / count_all.to_f
  end
end

str_1 = "良識はこの世のものでもっとも公平に配分されている"
str_2 = "良識はこの世でもっとも公平に分け与えられているものである"

puts "文１：#{str_1}"
puts "文２：#{str_2}"
puts "類似度(1-gram): #{str_1.sim_ngram(str_2, 1)}"
puts "類似度(2-gram): #{str_1.sim_ngram(str_2, 2)}"
puts "類似度(3-gram): #{str_1.sim_ngram(str_2)}"
puts "類似度(4-gram): #{str_1.sim_ngram(str_2, 4)}"