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module Enumerable
# Collect an enumerable into sets, grouped by the result of a block. Useful,
# for example, for grouping records by date.
#
# e.g.
#
# latest_transcripts.group_by(&:day).each do |day, transcripts|
# p "#{day} -> #{transcripts.map(&:class) * ', '}"
# end
# "2006-03-01 -> Transcript"
# "2006-02-28 -> Transcript"
# "2006-02-27 -> Transcript, Transcript"
# "2006-02-26 -> Transcript, Transcript"
# "2006-02-25 -> Transcript"
# "2006-02-24 -> Transcript, Transcript"
# "2006-02-23 -> Transcript"
def group_by
inject({}) do |groups, element|
(groups[yield(element)] ||= []) << element
groups
end
end if RUBY_VERSION < '1.9'
# Calculates a sum from the elements. Examples:
#
# payments.sum { |p| p.price * p.tax_rate }
# payments.sum(&:price)
#
# This is instead of payments.inject { |sum, p| sum + p.price }
#
# Also calculates sums without the use of a block:
# [5, 15, 10].sum # => 30
#
# The default identity (sum of an empty list) is zero.
# However, you can override this default:
#
# [].sum(Payment.new(0)) { |i| i.amount } # => Payment.new(0)
#
def sum(identity = 0, &block)
return identity unless size > 0
if block_given?
map(&block).sum
else
inject { |sum, element| sum + element }
end
end
# Convert an enumerable to a hash. Examples:
#
# people.index_by(&:login)
# => { "nextangle" => <Person ...>, "chade-" => <Person ...>, ...}
# people.index_by { |person| "#{person.first_name} #{person.last_name}" }
# => { "Chade- Fowlersburg-e" => <Person ...>, "David Heinemeier Hansson" => <Person ...>, ...}
#
def index_by
inject({}) do |accum, elem|
accum[yield(elem)] = elem
accum
end
end
end
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