Module: Enumerable

Included in:
AntMapper::Errors
Defined in:
lib/ant_support/core_ext/enumerable.rb

Instance Method Summary collapse

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/ant_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/ant_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.

Returns:

  • (Boolean) 


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# File 'lib/ant_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/ant_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