Methods
Public Instance methods
Collect an enumerable into sets, grouped by the result of a block. Useful, for example, for grouping records by date.
e.g.
latest_transcripts.group_by(&:day).each do |day, transcripts|
p "#{day} -> #{transcripts.map(&:class) * ', '}"
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"
[ show source ]
# File vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb, line 17
17: def group_by
18: inject({}) do |groups, element|
19: (groups[yield(element)] ||= []) << element
20: groups
21: end
22: end
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 ...>, ...}
[ show source ]
# File vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb, line 55
55: def index_by
56: inject({}) do |accum, elem|
57: accum[yield(elem)] = elem
58: accum
59: end
60: end
Calculates a sum from the elements. Examples:
payments.sum { |p| p.price * p.tax_rate }
payments.sum(&:price)
This is instead of payments.inject { |sum, p| sum + p.price }
Also calculates sums without the use of a block:
[5, 15, 10].sum # => 30
The default identity (sum of an empty list) is zero. However, you can override this default:
[].sum(Payment.new(0)) { |i| i.amount } # => Payment.new(0)
[ show source ]
# File vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb, line 39
39: def sum(identity = 0, &block)
40: return identity unless size > 0
41: if block_given?
42: map(&block).sum
43: else
44: inject { |sum, element| sum + element }
45: end
46: end