Class: Bmg::Operator::Project

Inherits:
Object
  • Object
show all
Includes:
Unary
Defined in:
lib/bmg/operator/project.rb

Overview

Project operator.

Projects operand’s tuples on given attributes, that is, keep those attributes only. The operator takes care of removing duplicates.

Example:

[{ a: 1, b: 2 }] project [:b] => [{ b: 2 }]

All attributes in the attrlist SHOULD be existing attributes of the input tuples.

Instance Attribute Summary

Attributes included from Bmg::Operator

#type

Instance Method Summary collapse

Methods included from Unary

#bind

Methods included from Bmg::Operator

#inspect, #to_s

Methods included from Relation

#_count, #bind, #count, #debug, empty, #empty?, new, #one, #one_or_nil, #to_csv, #to_json, #to_xlsx, #type, #visit, #with_type, #with_type_attrlist, #with_typecheck, #without_typecheck, #y_by_x, #ys_by_x

Methods included from Algebra

#allbut, #autosummarize, #autowrap, #constants, #extend, #group, #image, #join, #left_join, #matching, #materialize, #minus, #not_matching, #page, #project, #rename, #restrict, #spied, #summarize, #transform, #ungroup, #union, #unspied, #unwrap

Methods included from Algebra::Shortcuts

#cross_product, #exclude, #image, #images, #join, #left_join, #matching, #not_matching, #prefix, #rxmatch, #suffix, #ungroup, #unwrap, #where

Constructor Details

#initialize(type, operand, attrlist) ⇒ Project

Returns a new instance of Project.



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# File 'lib/bmg/operator/project.rb', line 19

def initialize(type, operand, attrlist)
  @type = type
  @operand = operand
  @attrlist = attrlist
end

Instance Method Details

#delete(predicate = Predicate.tautology) ⇒ Object 



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# File 'lib/bmg/operator/project.rb', line 56

def delete(predicate = Predicate.tautology)
  operand.delete(predicate)
end

#each ⇒ Object 



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# File 'lib/bmg/operator/project.rb', line 31

def each
  return to_enum unless block_given?
  seen = {}
  @operand.each do |tuple|
    projected = tuple_project(tuple)
    unless seen.has_key?(projected)
      yield(projected)
      seen[projected] = true
    end
  end
end

#insert(arg) ⇒ Object 



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# File 'lib/bmg/operator/project.rb', line 43

def insert(arg)
  case arg
  when Hash       then operand.insert(valid_tuple!(arg))
  when Enumerable then operand.insert(arg.map{|t| valid_tuple!(t) })
  else
    super
  end
end

#to_ast ⇒ Object 



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# File 'lib/bmg/operator/project.rb', line 60

def to_ast
  [ :project, operand.to_ast, attrlist ]
end

#update(tuple, predicate = Predicate.tautology) ⇒ Object 



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# File 'lib/bmg/operator/project.rb', line 52

def update(tuple, predicate = Predicate.tautology)
  operand.update(valid_tuple!(tuple), predicate)
end