class SPARQL::Algebra::Operator::Avg

The SPARQL `avg` set function.

@example

(prefix ((: <http://www.example.org/>))
  (project (?avg)
    (extend ((?avg ??.0))
      (group () ((??.0 (avg ?o)))
        (bgp (triple ?s :dec ?o))))))

@see www.w3.org/TR/sparql11-query/#defn_aggAvg

Constants

NAME

Public Class Methods

new(*operands, **options) click to toggle source
Calls superclass method SPARQL::Algebra::Operator::new
# File lib/sparql/algebra/operator/avg.rb, line 19
def initialize(*operands, **options)
  raise ArgumentError,
    "avg operator accepts at most one argument with an optional :distinct" if
    (operands - %i{distinct}).length != 1
  super
end

Public Instance Methods

apply(enum, **options) click to toggle source

The Avg set function calculates the average value for an expression over a group. It is defined in terms of Sum and Count.

@param [Enumerable<Array<RDF::Term>>] enum

enum of evaluated operand

@return [RDF::Literal::Numeric] The numeric average of the terms

# File lib/sparql/algebra/operator/avg.rb, line 32
def apply(enum, **options)
  # FIXME: we don't actually do anything with distinct
  operands.shift if distinct = (operands.first == :distinct)
  if enum.empty?
    RDF::Literal(0)
  elsif enum.flatten.all? {|n| n.is_a?(RDF::Literal::Numeric)}
    enum.flatten.reduce(:+) / RDF::Literal::Decimal.new(enum.length)
  else
    raise TypeError, "Averaging non-numeric types: #{enum.flatten}"
  end
end