Contents

module Generators

  module Weights

    # Uses a logarithmic weight.
    # If for a key k we have x ids, the weight is:
    # w(x): log(x)
    # Special case: If x < 1, then we use 0.
    #
    class Logarithmic < Strategy

      # Generates a partial index from the given inverted index.
      #
      def generate_from inverted
        inverted.inject({}) do |hash, text_ids|
          text, ids = *text_ids
          weight = weight_for ids.size
          hash[text] ||= weight.round(2) if weight
          hash
        end
      end

      # Sets the weight value.
      #
      # If the size is 0 or one, we would get -Infinity or 0.0.
      # Thus we do not set a value if there is just one. The default, dynamically, is 0.
      #
      # BUT: We need the value, even if 0. To designate that there is a weight!
      #
      def weight_for amount
        return 0 if amount < 1
        Math.log amount
      end

    end

  end

end

Version data entries

1 entries across 1 versions & 1 rubygems

Version	Path
picky-2.7.0	lib/picky/generators/weights/logarithmic.rb