Ruby, merging lazy sequences

Question

Let i have lazy sequences: s1, s2, s3, ..., sN, with non-descending numbers, for example:

s1 = [1, 1, 2, 3, 3, 3, 4, .....] s2 = [1, 2, 2, 2, 2, 2, 3, 3, 4, ....] s3 = [1, 2, 3, 3, 3, 3, 4, 4, 4, ....]

what I'd like to do - is to merge it, grouping by similar items and processing it with some function, for example generate list of tuples (number, count)

for my case:

merge(s1, s2, s3) should generate [ [1, 4], [2, 6], [3, 9], [4, 5], .... ]

Are any gems, etc., to process such sequences

@MarkThomas I didn't see the word *lazy*.. Thanks for pointing me. — Arup Rakshit, May 14 '14 at 12:12

Uri Agassi · Answer 1 · 2014-05-14T11:48:50.920

If you want to do it lazily, here is some code which would do that:

def merge(*args)
  args.map!(&:lazy)
  Enumerator.new do |yielder| 
    while num = args.map(&:peek).min
      count = 0
      while list = args.find { |l| l.peek == num }
        list.next
        list.peek rescue args.delete list

        count += 1
      end
      yielder.yield [num, count]
    end
  end
end

s1 = [1, 1, 2, 3, 3, 3, 4] 
s2 = [1, 2, 2, 2, 2, 2, 3, 3, 4] 
s3 = [1, 2, 3, 3, 3, 3, 4, 4, 4]
s4 = (0..1.0/0)

merge(s1, s2, s3, s4).take(20)
# => [[0, 1], [1, 5], [2, 8], [3, 10], [4, 6], [5, 1], [6, 1], [7, 1], [8, 1], [9, 1], [10, 1], [11, 1], [12, 1], [13, 1], [14, 1], [15, 1], [16, 1], [17, 1], [18, 1], [19, 1]]

Ruby, merging lazy sequences

1 Answers1