Oliver Legg
October 14, 2013
590

# Enumerators

October 14, 2013

## Transcript

2. ### Enumerable #all? #any? #chunk #collect #collect_concat #count #cycle #detect #drop

#drop_while #each_cons #each_entry #each_slice #each_with_index #each_with_object #entries #find #find_all #find_index #first #flat_map #grep #group_by #include? #inject #lazy #map #max #max_by #min_by #minmax #minmax_by #none? #one? #partition #reduce #reject #reverse_each #select #slice_before #sort #sort_by #take #take_while #to_a #zip

#with_object
4. ### enumerator = [1, 2, 3].each # => #<Enumerator: [1, 2,

3]:each> enumerator = [1, 2, 3].to_enum # => #<Enumerator: [1, 2, 3]:each> enumerator = [1, 2, 3].enum_for(:each) # => #<Enumerator: [1, 2, 3]:each>
5. ### def counter yield 1 yield 2 yield 3 end enumerator

= enum_for(:counter) enumerator.to_a # => [1, 2, 3]

7. ### letters = ['a', 'a', 'a', 'b', 'b', 'c'] counts =

letters.inject({}) do |memo, letter| memo[letter] ||= 0 memo[letter] += 1 memo end # => {"a"=>3, "b"=>2, "c"=>1}
8. ### letters = ['a', 'a', 'a', 'b', 'b', 'c'] counts =

letters.each.with_object({}) do |letter, memo| memo[letter] ||= 0 memo[letter] += 1 end # => {"a"=>3, "b"=>2, "c"=>1}
9. ### range = (1..10) range.map.with_index {|n, i| n * i }

# => [0, 2, 6, 12, 20, 30, 42, 56, 72, 90] range.select.with_index {|_, i| i.even? } # => [1, 3, 5, 7, 9]

11. ### enumerator = [1, 2, 3].each # => #<Enumerator: [1, 2,

3]:each> enumerator.next # => 1 enumerator.next # => 2 enumerator.next # => 3 enumerator.next # StopIteration: iteration reached an end
12. ### enumerator = [1, 2, 3].to_enum # => #<Enumerator: [1, 2,

3]:each> enumerator.peek # => 1 enumerator.peek # => 2 enumerator.peek # => 3 enumerator.next # => 1
13. ### loop do i = enumerator.next puts i # `loop` silently

rescues StopIteration end

15. ### fibonacci = Enumerator.new(Float::INFINITY) do |yielder| a, b = 0, 1

loop do yielder.yield a a, b = b, (a + b) end end
16. ### class SumOfNaturalNumbers < Enumerator def initialize super(Float::INFINITY) do |yielder| n

= 1 loop do yielder.yield (n * (n + 1)) / 2 n += 1 end end end end
17. ### def fibonacci a, b = 0, 1 loop do yield

a a, b = b, (a + b) end end enumerator = enum_for(:fibonacci) # => #<Enumerator: main:fibonacci>

19. ### require 'prime' primes = Prime.instance primes .select {|i| i.to_s.end_with?('3') }

.take(10) # infinite loop
20. ### require 'prime' primes = Prime.instance primes .lazy .select {|i| i.to_s.end_with?('3')

} .take(10) .to_a # => [3, 13, 23, 43, 53, 73, 83, 103, 113, 163]

.to_a
22. ### mine = ->(repository) { repository.owner == 'olly' } cutoff =

(Time.now - (365 * 24 * 60 * 60)).to_datetime year_old = ->(repository) { repository.commits.first.date > cutoff } client.repositories .lazy .select(&mine) .select(&year_old) .take(10) .each {|repository| puts repository.name }