How may i fetch next and before current element from array while iterating array with each.
array.each do |a|
# I want to fetch next and before current element.
end
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krunal shah
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1Two questions: 1) What is the "previous" element at the beginning and the "next" element at the end? 2) Should the `next` element be the `current` element of the next iteration (that is, after the group `[ar[4], ar[5], ar[6]]`, should the next group be `[ar[5], ar[6], ar[7]]` or `[ar[7], ar[8], ar[9]]`)? – Chuck Sep 29 '10 at 19:31
2 Answers
41
Take look at Enumerable#each_cons method:
[nil, *array, nil].each_cons(3){|prev, curr, nxt|
puts "prev: #{prev} curr: #{curr} next: #{nxt}"
}
prev: curr: a next: b
prev: a curr: b next: c
prev: b curr: c next:
If you like, you can wrap it in new Array method:
class Array
def each_with_prev_next &block
[nil, *self, nil].each_cons(3, &block)
end
end
#=> nil
array.each_with_prev_next do |prev, curr, nxt|
puts "prev: #{prev} curr: #{curr} next: #{nxt}"
end
David Chouinard
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Mladen Jablanović
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Great! I hate `+` variant, but I thought there isn't anything prettier. I'll update the answer if you don't mind. – Mladen Jablanović Sep 30 '10 at 04:58
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if someone is looking for a way to "map" the elements instead of just iterate over them you can do something like `1..9).each_cons(2).map { |a| a }` – equivalent8 Nov 08 '15 at 00:25
14
You can use Enumerable#each_with_index to get the index of each element as you iterate, and use that to get the surrounding items.
array.each_with_index do |a, i|
prev_element = array[i-1] unless i == 0
next_element = array[i+1] unless i == array.size - 1
end
cweston
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Daniel Vandersluis
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