Module: Enumerable
- Included in:
- ActiveObject::Errors
- Defined in:
- lib/active_support/core_ext/enumerable.rb
Instance Method Summary collapse
-
#each_with_object(memo, &block) ⇒ Object
Iterates over a collection, passing the current element and the
memo
to the block. -
#index_by ⇒ Object
Convert an enumerable to a hash.
-
#many?(&block) ⇒ Boolean
Returns true if the collection has more than 1 element.
-
#sum(identity = 0, &block) ⇒ Object
Calculates a sum from the elements.
Instance Method Details
#each_with_object(memo, &block) ⇒ Object
Iterates over a collection, passing the current element and the memo
to the block. Handy for building up hashes or reducing collections down to one object. Examples:
%w(foo bar).each_with_object({}) { |str, hsh| hsh[str] = str.upcase } #=> {'foo' => 'FOO', 'bar' => 'BAR'}
Note that you can’t use immutable objects like numbers, true or false as the memo. You would think the following returns 120, but since the memo is never changed, it does not.
(1..5).each_with_object(1) { |value, memo| memo *= value } # => 1
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# File 'lib/active_support/core_ext/enumerable.rb', line 44 def each_with_object(memo, &block) returning memo do |m| each do |element| block.call(element, m) end end end |
#index_by ⇒ Object
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 ...>, ...}
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# File 'lib/active_support/core_ext/enumerable.rb', line 59 def index_by inject({}) do |accum, elem| accum[yield(elem)] = elem accum end end |
#many?(&block) ⇒ Boolean
Returns true if the collection has more than 1 element. Functionally equivalent to collection.size > 1. Works with a block too ala any?, so people.many? { |p| p.age > 26 } # => returns true if more than 1 person is over 26.
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# File 'lib/active_support/core_ext/enumerable.rb', line 68 def many?(&block) size = block_given? ? select(&block).size : self.size size > 1 end |
#sum(identity = 0, &block) ⇒ Object
Calculates a sum from the elements. Examples:
payments.sum { |p| p.price * p.tax_rate }
payments.sum(&:price)
The latter is a shortcut for:
payments.inject { |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)
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# File 'lib/active_support/core_ext/enumerable.rb', line 22 def sum(identity = 0, &block) return identity unless size > 0 if block_given? map(&block).sum else inject { |sum, element| sum + element } end end |