Class: SPARQL::Algebra::Operator::Count

Inherits:
SPARQL::Algebra::Operator show all
Includes:
Aggregate
Defined in:
lib/sparql/algebra/operator/count.rb

Overview

The SPARQL count set function.

[127] Aggregate::= ‘COUNT’ ‘(’ ‘DISTINCT’? ( ‘*’ | Expression ) ‘)’ …

Examples:

SPARQL Grammar

PREFIX : <http://www.example.org/>
SELECT (COUNT(?O) AS ?C)
WHERE { ?S ?P ?O }

SSE

(prefix ((: <http://www.example.org/>))
  (project (?C)
    (extend ((?C ??.0))
      (group () ((??.0 (count ?O)))
        (bgp (triple ?S ?P ?O))))))

SPARQL Grammar (count(*))

PREFIX : <http://www.example.org>

SELECT (COUNT(*) AS ?C)
WHERE { ?S ?P ?O }

SSE (count(*))

(prefix
 ((: <http://www.example.org>))
 (project (?C)
  (extend ((?C ??.0))
   (group () ((??.0 (count)))
    (bgp (triple ?S ?P ?O))))))

SPARQL Grammar (count(distinct *))

PREFIX : <http://www.example.org>

SELECT (COUNT(DISTINCT *) AS ?C)
WHERE { ?S ?P ?O }

SSE (count(distinct *))

(prefix
 ((: <http://www.example.org>))
 (project (?C)
  (extend ((?C ??.0))
   (group () ((??.0 (count distinct)))
    (bgp (triple ?S ?P ?O))))))

See Also:

Constant Summary collapse

NAME = 
:count

Constants inherited from SPARQL::Algebra::Operator

ARITY, IsURI, URI

Constants included from Expression

Expression::PATTERN_PARENTS

Instance Attribute Summary

Attributes inherited from SPARQL::Algebra::Operator

#operands

Instance Method Summary collapse

Methods included from Aggregate

#aggregate, #replace_aggregate!, #replace_vars!

Methods inherited from SPARQL::Algebra::Operator

#aggregate?, arity, #base_uri, base_uri, base_uri=, #bind, #boolean, #constant?, #deep_dup, #each_descendant, #eql?, #evaluatable?, evaluate, #executable?, #first_ancestor, for, #initialize, #inspect, #ndvars, #node?, #operand, #optimize, #optimize!, #parent, #parent=, #prefixes, prefixes, prefixes=, #rewrite, #to_binary, to_sparql, #to_sxp, #to_sxp_bin, #validate!, #variable?, #variables, #vars

Methods included from Expression

cast, #constant?, #evaluate, extension, extension?, extensions, for, #invalid?, new, #node?, open, #optimize, #optimize!, parse, register_extension, #to_sxp_bin, #valid?, #validate!, #variable?

Constructor Details

This class inherits a constructor from SPARQL::Algebra::Operator

Instance Method Details

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

Count is a SPARQL set function which counts the number of times a given expression has a bound, and non-error value within the aggregate group.

Parameters:

Returns:

  • (RDF::Literal::Integer) —

    The number of non-error terms in the multiset



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# File 'lib/sparql/algebra/operator/count.rb', line 60

def apply(enum, **options)
  RDF::Literal(enum.length)
end

#to_sparql(**options) ⇒ String

Returns a partial SPARQL grammar for this operator.

Returns:

  • (String) 


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# File 'lib/sparql/algebra/operator/count.rb', line 69

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