Question

If I want to interleave a set of arrays in Ruby, and each array was the same length, we could do so as:

a.zip(b).zip(c).flatten

However, how do we solve this problem if the arrays can be different sizes?

We could do something like:

def interleave(*args)
  raise 'No arrays to interleave' if args.empty?
  max_length = args.inject(0) { |length, elem| length = [length, elem.length].max }
  output = Array.new
  for i in 0...max_length
    args.each { |elem|
      output << elem[i] if i < elem.length
    }
  end
  return output
end

But is there a better ‘Ruby’ way, perhaps using zip or transpose or some such?

Answer 1

If the source arrays don’t have nil in them, you only need to extend the first array with nils, zip will automatically pad the others with nil. This also means you get to use compact to clean the extra entries out which is hopefully more efficient than explicit loops

def interleave(a,*args)
    max_length = args.map(&:size).max
    padding = [nil]*[max_length-a.size, 0].max
    (a+padding).zip(*args).flatten.compact
end

Here is a slightly more complicated version that works if the arrays do contain nil

def interleave(*args)
    max_length = args.map(&:size).max
    pad = Object.new()
    args = args.map{|a| a.dup.fill(pad,(a.size...max_length))}
    ([pad]*max_length).zip(*args).flatten-[pad]
end