Class: SPARQL::Algebra::Operator::Sum

Inherits:
Operator
  • Object
show all
Includes:
Aggregate
Defined in:
lib/sparql/algebra/operator/sum.rb

Overview

The SPARQL sum set function.

[127] Aggregate::= ... | 'SUM' '(' 'DISTINCT'? Expression ')'

Examples:

SPARQL Grammar

PREFIX : <http://www.example.org/>
SELECT (SUM(?o) AS ?sum)
WHERE { ?s :dec ?o }

SSE

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

See Also:

Constant Summary collapse

NAME = 
:sum

Instance Method Summary collapse

Methods included from Aggregate

#aggregate, #replace_aggregate!, #replace_vars!

Instance Method Details

#apply(enum, **options) ⇒ RDF::Literal::Numeric

Sum is a SPARQL set function that will return the numeric value obtained by summing the values within the aggregate group. Type promotion happens as per the op:numeric-add function, applied transitively, (see definition below) so the value of SUM(?x), in an aggregate group where ?x has values 1 (integer), 2.0e0 (float), and 3.0 (decimal) will be 6.0 (float).

Parameters:

Returns:

  • (RDF::Literal::Numeric) —

    The sum of the terms



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# File 'lib/sparql/algebra/operator/sum.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(:+)
  else
    raise TypeError, "Averaging non-numeric types: #{enum.flatten}"
  end
end

#to_sparql(**options) ⇒ String

Returns a partial SPARQL grammar for this operator.

Returns:

  • (String) 


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# File 'lib/sparql/algebra/operator/sum.rb', line 49

def to_sparql(**options)
  distinct = operands.first == :distinct
  args = distinct ? operands[1..-1] : operands
  "SUM(#{'DISTINCT ' if distinct}#{args.to_sparql(**options)})"
end