Module: Enumerable

Defined in:
lib/active_support/json/encoding.rb,
lib/active_support/core_ext/enumerable.rb

Instance Method Summary collapse

Instance Method Details

#as_json(options = nil) ⇒ Object

:nodoc:


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# File 'lib/active_support/json/encoding.rb', line 185

def as_json(options = nil) to_a end

#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 78

def each_with_object(memo, &block)
  each do |element|
    block.call(element, memo)
  end
  memo
end

#exclude?(object) ⇒ Boolean

The negative of the Enumerable#include?. Returns true if the collection does not include the object.

Returns:

  • (Boolean)

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# File 'lib/active_support/core_ext/enumerable.rb', line 107

def exclude?(object)
  !include?(object)
end

#group_byObject

Collect an enumerable into sets, grouped by the result of a block. Useful, for example, for grouping records by date.

Example:

latest_transcripts.group_by(&:day).each do |day, transcripts|
  p "#{day} -> #{transcripts.map(&:class).join(', ')}"
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"

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# File 'lib/active_support/core_ext/enumerable.rb', line 22

def group_by
  assoc = ActiveSupport::OrderedHash.new

  each do |element|
    key = yield(element)

    if assoc.has_key?(key)
      assoc[key] << element
    else
      assoc[key] = [element]
    end
  end

  assoc
end

#index_byObject

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 92

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.

Returns:

  • (Boolean)

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# File 'lib/active_support/core_ext/enumerable.rb', line 101

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(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)

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# File 'lib/active_support/core_ext/enumerable.rb', line 57

def sum(identity = 0, &block)
  if block_given?
    map(&block).sum(identity)
  else
    inject { |sum, element| sum + element } || identity
  end
end