module Company
  module Mapping

# NormalizedTermFrequency inherits from TermFrequency class. It calculates Term Frequency as
# logarithmically scaled frequency: tf(t,d) = 1 + log(f(t,d)), or zero if
# f(t,d) is zero.

    class NormalizedTermFrequency < TermFrequency

      def calculate(text)
        _rawTF = rawFrequency(text)
        _logTF = Hash.new

        _rawTF.each do |key, value|
          _logTF[key] = 1.0 + Math.log(value)
        end

        return _logTF
      end

      def info
        return "Logarithmically scaled term frequency: tf(t,d) = 1 + log(f(t,d)), or zero if ft,d is zero";
      end
    end

  end
end