Class: RDF::N3::Algebra::List::Iterate

Inherits:
RDF::N3::Algebra::ListOperator show all
Defined in:
lib/rdf/n3/algebra/list/iterate.rb

Overview

Generates a list of lists when each constituent list is composed of the index and value of each element in the subject.

Binds variables in the object list.

Examples:

{ (1 2 3) list:iterate ((0 1) (1 2) (2 3)) } => { :test4a a :SUCCESS }.

Constant Summary collapse

NAME = 
:listIterate
URI = 
RDF::N3::List.iterate

Instance Attribute Summary

Attributes included from Enumerable

#existentials, #universals

Instance Method Summary collapse

Methods inherited from RDF::N3::Algebra::ListOperator

#as_literal, #input_operand, #resolve, #validate

Methods included from Builtin

#each, #evaluate, #hash, #input_operand, #rank, #to_uri

Instance Method Details

#execute(queryable, solutions:, **options) ⇒ RDF::Query::Solutions

Evaluates this operator using the given variable bindings. The subject MUST evaluate to a list and the object to a list composed of two components: index and value.

Examples:

{(1 2 3) list:iterate (?x ?y)} => {:solution :is (?x ?y)} .
{(1 2 3) list:iterate ?L} => {:solution :is ?L} .
{(1 2 3) list:iterate (1 ?y)} => {:value :is ?y} .
{(1 2 3) list:iterate (?x 2)} => {:index :is ?x} .

Parameters:

  • queryable (RDF::Queryable) —

    the graph or repository to query

  • solutions (RDF::Query::Solutions) —

    solutions for chained queries

Returns:

  • (RDF::Query::Solutions) 


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# File 'lib/rdf/n3/algebra/list/iterate.rb', line 34

def execute(queryable, solutions:, **options)
  RDF::Query::Solutions(solutions.map do |solution|
    subject = operand(0).evaluate(solution.bindings, formulae: formulae) || operand(0)
    # Might be a variable or node evaluating to a list in queryable, or might be a list with variables
    # If subject evaluated to a BNode, re-expand as a list
    subject = RDF::N3::List.try_list(subject, queryable).evaluate(solution.bindings, formulae: formulae)
    next unless validate(subject)

    object = operand(1).evaluate(solution.bindings, formulae: formulae) || operand(1)
    next unless object
    # If object evaluated to a BNode, re-expand as a list
    object = RDF::N3::List.try_list(object, queryable).evaluate(solution.bindings, formulae: formulae) || object

    if object.list? && object.variable?
      # Create a solution for those entries in subject that match object
      if object.length != 2
        log_error(NAME) {"object is not a list with two entries: #{object.to_sxp}"}
        next
      end
      if object.first.variable? && object.last.variable?
        solutions = RDF::Query::Solutions.new
        subject.each_with_index do |r, i|
          s = solution.merge(object.first.to_sym => RDF::Literal(i), object.last.to_sym => r)
          log_debug(self.class.const_get(:NAME), "result: #{s.to_sxp}")
          solutions << s
        end
        solutions
      elsif object.first.variable?
        # Solution binds indexes to all matching values
        solutions = RDF::Query::Solutions.new
        subject.each_with_index do |r, i|
          next unless r == object.last
          s = solution.merge(object.first.to_sym => RDF::Literal(i))
          log_debug(self.class.const_get(:NAME), "result: #{s.to_sxp}")
          solutions << s
        end
        solutions
      elsif object.last.variable?
        # Solution binds value at specified index
        next unless v = subject.at(object.first)
        s = solution.merge(object.last.to_sym => v)
        log_debug(self.class.const_get(:NAME), "result: #{s.to_sxp}")
        s
      end
    elsif object.variable?
      # Create a solution for each index/value pair in subject
      solutions = RDF::Query::Solutions.new
      subject.each_with_index do |r, i|
        s = solution.merge(object.to_sym => RDF::N3::List[RDF::Literal(i), r])
        log_debug(self.class.const_get(:NAME), "result: #{s.to_sxp}")
        solutions << s
      end
      solutions
    else
      # Evaluates to true if the subject has a matching entry
      same = subject.at(object.first) == object.last
      log_debug(self.class.const_get(:NAME), "result: #{same.inspect}")
      solution if same
    end
  end.flatten.compact.uniq)
end