Weighted Tanimoto algorithm

"weighted" tanimoto

# weighted tanimoto for taggables
#  works with acts_as_taggable_on_steroids, 
#  assuming you have a weight attribute in your Tagging model

def tanimoto(a,b)
  a_size = a.taggings.map { |t| t.weight}.sum
  b_size = b.taggings.map { |t| t.weight}.sum
  return 0 if (a_size == 0 || b_size == 0)
  c_size = a.taggings.map { |t| b.tag_list.include?(t.name) ? [t.weight, b.taggings.find_by_tag_id(t.tag_id).weight].min : 0 }.sum
   
  coefficient = (c_size.to_f/(a_size + b_size - c_size))
end