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Enumerators

 Enumerators

7a7a5a9574e745f49a65aaa6a93df3c8?s=128

Oliver Legg

October 14, 2013
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  1. ENumerators

  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
  3. Enumerator #each #feed #next #next_values #peek #peek_values #rewind #size #with_index

    #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]
  6. with_object with_index

  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]
  10. Iterator

  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
  14. Generator

  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>
  18. LAZY

  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]
  21. File.open('/usr/share/dict/words') .each_line .lazy .map(&:chomp) .take_while {|line| line.length < 10 }

    .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 }