Module: Enumerable

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

Instance Method Summary collapse

Instance Method Details

#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 20

def group_by
  inject ActiveSupport::OrderedHash.new do |grouped, element|
    (grouped[yield(element)] ||= []) << element
    grouped
  end
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 63

def index_by
  inject({}) do |accum, elem|
    accum[yield(elem)] = elem
    accum
  end
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 46

def sum(identity = 0, &block)
  return identity unless size > 0

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

#to_json(options = {}) ⇒ Object

Returns a JSON string representing the enumerable. Any options given will be passed on to its elements. For example:

users = User.find(:all)
# => users.to_json(:only => :name)

will pass the :only => :name option to each user.


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# File 'lib/active_support/json/encoders/enumerable.rb', line 9

def to_json(options = {}) #:nodoc:
  "[#{map { |value| ActiveSupport::JSON.encode(value, options) } * ', '}]"
end