How to iterate over an array in overlapping groups of n elements?

Question

Say you have this array:

arr = w|one two three|

How can I iterate over it by having two consecutive elements as block arguments like this:

1st cycle: |nil, 'one'|
2nd cycle: |'one', 'two'|
3rd cycle: |'two', 'three'|

Sofar I came only with this:

arr.each_index { |i| [i - 1 < 0 ? nil: arr[i - 1], arr[i]] }

Any better solutions? Is there something like each(n)?

score 9 · Accepted Answer · answered Dec 04 '14 at 09:00

9

You can add nil as the first element of your arr and use Enumerable#each_cons method:

arr.unshift(nil).each_cons(2).map { |first, second| [first, second] }
# => [[nil, "one"], ["one", "two"], ["two", "three"]]

(I'm using map here to show what exactly is returned on each iteration)

answered Dec 04 '14 at 09:00

Marek Lipka

That's exactly what I was looking for. I was sure there's something like that, I just didn't know it. Thank you :) – Alexander Popov Dec 04 '14 at 09:01
1

nice. but probably not change the original array. `([nil] + arr).each_const(2)` – SHS Dec 04 '14 at 15:20

score 5 · Answer 2 · answered Dec 04 '14 at 09:05

5

> [1, 2, 3, 4, 5, 6, 7, 8, 9].each_cons(2).to_a
# => [[1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8], [8, 9]]

answered Dec 04 '14 at 09:05

Hetal Khunti

2 Answers2