Contents

module Alf
  class Aggregator
  
    # 
    # Defines a COUNT aggregation operator
    #
    class Count < Aggregator
      def least(); 0; end
      def happens(memo, tuple) memo + 1; end
    end # class Count
  
    # 
    # Defines a SUM aggregation operator
    #
    class Sum < Aggregator
      def least(); 0; end
      def _happens(memo, val) memo + val; end
    end # class Sum
  
    # 
    # Defines an AVG aggregation operator
    #
    class Avg < Aggregator
      def least(); [0.0, 0.0]; end
      def _happens(memo, val) [memo.first + val, memo.last + 1]; end
      def finalize(memo) memo.first / memo.last end
    end # class Sum
  
    # 
    # Defines a MIN aggregation operator
    #
    class Min < Aggregator
      def least(); nil; end
      def _happens(memo, val) 
        memo.nil? ? val : (memo < val ? memo : val) 
      end
    end # class Min
  
    # 
    # Defines a MAX aggregation operator
    #
    class Max < Aggregator
      def least(); nil; end
      def _happens(memo, val) 
        memo.nil? ? val : (memo > val ? memo : val) 
      end
    end # class Max
    
    #
    # Defines a COLLECT aggregation operator
    #
    class Collect < Aggregator
      def least(); []; end
      def _happens(memo, val) 
        memo << val
      end
    end
  
    # 
    # Defines a CONCAT aggregation operator
    # 
    class Concat < Aggregator
      def least(); ""; end
      def default_options
        {:before => "", :after => "", :between => ""}
      end
      def _happens(memo, val) 
        memo << options[:between].to_s unless memo.empty?
        memo << val.to_s
      end
      def finalize(memo)
        options[:before].to_s + memo + options[:after].to_s
      end
    end
  
  end # class Aggregator
end # module Alf

Version data entries

1 entries across 1 versions & 1 rubygems

Version	Path
alf-0.10.0	lib/alf/aggregator/aggregators.rb