Sha256: a4c58bb86ea785acd1fe04f699aa97d838de28cd3ee8b7a14a166911749c7818
Contents?: true
Size: 1.87 KB
Versions: 31
Compression:
Stored size: 1.87 KB
Contents
module Bmg
module Operator
#
# Group operator.
#
# Groups some operand attributes as a new Relation-valued
# attribute
#
class Group
include Operator::Unary
DEFAULT_OPTIONS = {
# Whether we need to convert each group as an Array,
# instead of keeping a Relation instance
array: false
}
def initialize(type, operand, attrs, as, options)
@type = type
@operand = operand
@attrs = attrs
@as = as
@options = DEFAULT_OPTIONS.merge(options)
end
protected
attr_reader :attrs, :as, :options
public
def each(&bl)
return to_enum unless block_given?
index = Hash.new{|h,k| h[k] = k.merge(as => empty_group) }
operand.each do |tuple|
key = TupleAlgebra.allbut(tuple, attrs)
sub = TupleAlgebra.project(tuple, attrs)
index[key][as].operand << sub
end
if options[:array]
index.values.each do |tuple|
tuple[as] = tuple[as].to_a
yield(tuple)
end
else
index.values.each(&bl)
end
end
def to_ast
[ :group, operand.to_ast, attrs.dup, as, options.dup ]
end
protected ### optimization
def _restrict(type, predicate)
top, bottom = predicate.and_split([as])
if top == predicate
super
else
op = operand
op = op.restrict(bottom)
op = op.group(attrs, as, options)
op = op.restrict(top)
op
end
end
protected ### inspect
def args
[ attrs, as, options ]
end
private
def empty_group
Relation::InMemory.new(group_type, Set.new)
end
def group_type
operand.type.project(attrs)
end
end # class Extend
end # module Operator
end # module Bmg
Version data entries
31 entries across 31 versions & 1 rubygems