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Enumerable

Public Instance Methods

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 lib/active_support/core_ext/enumerable.rb, line 77
def each_with_object(memo, &block)
  memo.tap do |m|
    each do |element|
      block.call(element, m)
    end
  end
end
exclude?(object) click to toggle source

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

# File lib/active_support/core_ext/enumerable.rb, line 117
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 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 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 lib/active_support/core_ext/enumerable.rb, line 101
def many?(&block)
  size = block_given? ? select(&block).size : self.size
  size > 1
end
none?(&block) click to toggle source

Returns true if none of the elements match the given block.

success = responses.none? {|r| r.status / 100 == 5 }

This is a builtin method in Ruby 1.8.7 and later.

# File lib/active_support/core_ext/enumerable.rb, line 111
def none?(&block)
  !any?(&block)
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 { |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 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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