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Enumerable

Public Instance Methods

as_json(options = nil) click to toggle source
# File D:/Develope/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activesupport-3.0.9/lib/active_support/json/encoding.rb, line 202
def as_json(options = nil) to_a end
each_with_object(memo, &block) click to toggle source

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
# File D:/Develope/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activesupport-3.0.9/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) click to toggle source

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

# File D:/Develope/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activesupport-3.0.9/lib/active_support/core_ext/enumerable.rb, line 107
def exclude?(object)
  !include?(object)
end
group_by() click to toggle source

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"
# File D:/Develope/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activesupport-3.0.9/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_by() click to toggle source

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 ...>, ...}
# File D:/Develope/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activesupport-3.0.9/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) click to toggle source

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.

# File D:/Develope/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activesupport-3.0.9/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) click to toggle source

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)
# File D:/Develope/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activesupport-3.0.9/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

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