Method: Evoc::Evaluate.average_precision

Defined in:

lib/evoc/evaluate.rb

.average_precision(recommendation, expected_outcome) ⇒ Float

calculate the average precision of the result based on an expected outcome

Parameters:

• recommendation (Array) —

  a sorted array

• expected_outcome (Array) —

  an array of items

Returns:

• (Float) —

  the average precision

# File 'lib/evoc/evaluate.rb', line 281

def self.average_precision(recommendation,expected_outcome)
    raise Error.new "#average_precision has been deprecated, use #ap instead"
    if !expected_outcome.is_a?(Array) then expected_outcome = [expected_outcome] end
    if (expected_outcome.size > 0) & !recommendation.empty?
      average_precision = 0
      correct_items = []
      total_items_considered = []
      # sort rules by weight
      # we first group rules with equal weights
      # and then sort the groups by weight
      recommendation.each do |items|
        if !items.is_a?(Array) then items = [items] end
        if items.first.class != expected_outcome.first.class
            raise ArgumentError, "Expected outcome was of type #{expected_outcome.first.class}, while the item in the recommendation was of type #{items.first.class}"
        end
        # skip already considered items
        if (new_items = items - total_items_considered).size > 0
          new_items.each {|item| total_items_considered << item}
          if correct_in_rule = (items & expected_outcome)
            if correct_in_rule.size > 0
              # make sure that the new items havent already been added earlier
              new_correct = (correct_in_rule - correct_items)
              # add new items
              new_correct.each {|item| correct_items << item}
              change_in_recall = new_correct.size.to_r/expected_outcome.size
              precision_at_k = correct_items.size.to_r/total_items_considered.size
              average_precision += (precision_at_k * change_in_recall)
            end
          end
        end
      end
      average_precision.to_f
    else
      nil
    end
end