Returns the most likely version among multiple given hashes

correct_version.rb

#!/usr/bin/ruby
# Run with 
# $ ruby -r minitest/autorun $PROGRAM_NAME
#
# Returns the correct version among multiple given 
# hashes. In other words, which hash is the one 
# that most ressemble the other hashes ?
# 
# First a Hash has to be able to say 
# how similar it is to another one
class Hash

  # Returns a factor f between 0 and 1 that indicates 
  # the similarity factor of self to other
  #
  # Calculates the number of keys with the same values
  # then divide the result by the number of keys
  def similarity_to(other)
    sum = 0
    each_pair do |k, v|
      (sum = sum + 1) if v == other[k]
    end
    sum.fdiv(size)
  end
end

class SimilarityFactorTest < Minitest::Test
  def test_similarity
    h = {one: 1, two: 2, three: 3, four: 4}
    assert_equal 1, h.similarity_to({one: 1, two: 2, three: 3, four: 4})
    assert_equal 0.75, h.similarity_to({one: 1, two: 2, three: 0, four: 4})
    assert_equal 0.5, h.similarity_to({one: 0, two: 2, three: 0, four: 4})
    assert_equal 0.25, h.similarity_to({one: 0, two: 0, three: 0, four: 4})
    assert_equal 0.0, h.similarity_to({one: 0, two: 0, three: 0, four: 0})
  end
end

# Now to determine the correct version among a sample of hashes
#
# Let us say the operator x returns the similarity factor f
# between h1 and h2 (i.e: f = h1 x h2)
#
# fh1 = (h1 x (H1 + ... + hn)) / n
# fh2 = (h2 x (h1 + ... + hn)) / n
# fhn = (hn x (h1 + ... + hn)) / n
#
# Correct version = max(fh1, fh2, ....fhn)

def correct_version(*candidates)
  count = candidates.size
  candidates.map do |c|
    factor = (candidates.inject(0) do |acc, o|
      acc = acc + c.similarity_to(o)
    end).fdiv(count)
    [c, factor.round(4)]
  end.sort_by {|t| t.last}.reverse
end


class CorrectVersionTest < Minitest::Test
  def test_versions_sorting_by_correcteness
    h1 = {one: 1, two: 2, three: 3, four: 4}
    h2 = {one: 1, two: 2, three: 3, four: 4}
    h3 = {one: 1, two: 2, three: 3, four: 0}
    h4 = {one: 1, two: 2, three: 0, four: 4}
    h5 = {one: 1, two: 2, three: 0, four: 0}
    h6 = {one: 1, two: 0, three: 0, four: 0}
    h7 = {one: 0, two: 0, three: 0, four: 0}

    results =  correct_version(h1, h2, h3, h4, h5, h6, h7) 
    assert_equal [[h5, 0.6786], [h3, 0.6429], [h4, 0.6429], 
                  [h1, 0.6071], [h2, 0.6071], [h6, 0.5714], [h7, 0.3929]], 
                  results
  end
end