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module Enumerable
# Calculates a sum from the elements.
#
# payments.sum { |p| p.price * p.tax_rate }
# payments.sum(&:price)
#
# The latter is a shortcut for:
#
# payments.inject(0) { |sum, p| sum + p.price }
#
# It can also calculate the sum without the use of a block.
#
# [5, 15, 10].sum # => 30
# ['foo', 'bar'].sum # => "foobar"
# [[1, 2], [3, 1, 5]].sum => [1, 2, 3, 1, 5]
#
# The default sum of an empty list is zero. You can override this default:
#
# [].sum(Payment.new(0)) { |i| i.amount } # => Payment.new(0)
#
def sum(identity = 0, &block)
if block_given?
map(&block).sum(identity)
else
inject { |sum, element| sum + element } || identity
end
end
# Convert an enumerable to a hash.
#
# 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
if block_given?
Hash[map { |elem| [yield(elem), elem] }]
else
to_enum :index_by
end
end
# Returns true if the enumerable has more than 1 element. Functionally equivalent to enum.to_a.size > 1.
# Can be called with a block too, much like any?, so <tt>people.many? { |p| p.age > 26 }</tt> returns true if more than one person is over 26.
def many?
cnt = 0
if block_given?
any? do |element|
cnt += 1 if yield element
cnt > 1
end
else
any? { (cnt += 1) > 1 }
end
end
# The negative of the <tt>Enumerable#include?</tt>. Returns true if the collection does not include the object.
def exclude?(object)
!include?(object)
end
end
class Range #:nodoc:
# Optimize range sum to use arithmetic progression if a block is not given and
# we have a range of numeric values.
def sum(identity = 0)
if block_given? || !(first.is_a?(Integer) && last.is_a?(Integer))
super
else
actual_last = exclude_end? ? (last - 1) : last
if actual_last >= first
(actual_last - first + 1) * (actual_last + first) / 2
else
identity
end
end
end
end
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