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Contents
module Alf
module Engine
#
# Aggregates the whole operand according to a Summarization. The result contains
# only one tuple.
#
# Example:
#
# res = [
# {:name => "Jones", :price => 12.0, :id => 1},
# {:name => "Smith", :price => 10.0, :id => 2}
# ]
# agg = Summarization[:size => "count",
# :total => "sum{ price }"]
# Aggregate.new(res, agg).to_a
# # => [
# # {:size => 2, :total => 22.0}
# # ]
#
class Aggregate
include Cog
# @return [Enumerable] The operand
attr_reader :operand
# @return [Summarization] The summarization to use
attr_reader :summarization
# Creates an Aggregate instance
def initialize(operand, summarization, expr = nil, compiler = nil)
super(expr, compiler)
@operand = operand
@summarization = summarization
end
# (see Cog#each)
def _each
scope = tuple_scope
agg = operand.inject(@summarization.least) do |memo,tuple|
@summarization.happens(memo, scope.__set_tuple(tuple))
end
yield @summarization.finalize(agg)
end
def arguments
[ summarization ]
end
end # class Aggregate
end # module Engine
end # module Alf
Version data entries
5 entries across 5 versions & 1 rubygems