sonic-pi

Enumerable#sum

Calculates a sum from the elements.

 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)

Source | Google | Stack overflow