Contents

module Picky

  module Generators

    module Weights
      
      # Uses a logarithmic weight.
      #
      # If given a constant, this will be added to the 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
        
        def initialize constant = 0.0
          # Note: Optimisation since it is called
          # once per indexed object.
          #
          if constant == 0.0
            def weight_for amount
              return 0 if amount < 1
              Math.log(amount).round 3
            end
          else
            @constant = constant
            # 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 @constant if amount < 1
              @constant + Math.log(amount).round(3)
            end
          end
        end

      end

    end

  end

end

Version data entries

1 entries across 1 versions & 1 rubygems

Version	Path
picky-4.5.7	lib/picky/generators/weights/logarithmic.rb