Class: SPARQL::Algebra::Operator::Sample
- Inherits:
-
SPARQL::Algebra::Operator
- Object
- SPARQL::Algebra::Operator
- SPARQL::Algebra::Operator::Sample
- Includes:
- Aggregate
- Defined in:
- lib/sparql/algebra/operator/sample.rb
Overview
The SPARQL sample
set function.
[127] Aggregate::= … | ‘SAMPLE’ ‘(’ ‘DISTINCT’? Expression ‘)’
Constant Summary collapse
- NAME =
:sample
Constants inherited from SPARQL::Algebra::Operator
Constants included from Expression
Instance Attribute Summary
Attributes inherited from SPARQL::Algebra::Operator
Instance Method Summary collapse
-
#apply(enum, **options) ⇒ RDF::Term
Sample is a set function which returns an arbitrary value from the multiset passed to it.
-
#initialize(*operands, **options) ⇒ Sample
constructor
A new instance of Sample.
-
#to_sparql(**options) ⇒ String
Returns a partial SPARQL grammar for this operator.
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, #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
#initialize(*operands, **options) ⇒ Sample
Returns a new instance of Sample.
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# File 'lib/sparql/algebra/operator/sample.rb', line 33 def initialize(*operands, **) raise ArgumentError, "sample operator accepts at most one argument with an optional :distinct" if (operands - %i{distinct}).length != 1 super end |
Instance Method Details
#apply(enum, **options) ⇒ RDF::Term
Sample is a set function which returns an arbitrary value from the multiset passed to it.
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# File 'lib/sparql/algebra/operator/sample.rb', line 47 def apply(enum, **) enum.detect(lambda {raise TypeError, "Sampling an empty multiset"}) {|e| e.first}.first end |
#to_sparql(**options) ⇒ String
Returns a partial SPARQL grammar for this operator.
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# File 'lib/sparql/algebra/operator/sample.rb', line 56 def to_sparql(**) distinct = operands.first == :distinct args = distinct ? operands[1..-1] : operands "SAMPLE(#{'DISTINCT ' if distinct}#{args.to_sparql(**)})" end |