From: "Florian G. Pflug" <fgp@...>
Date: 2003-05-30T21:33:28+09:00
Subject: Re: Iteration - last detection

On Fri, May 30, 2003 at 04:14:49AM +0900, Orion Hunter wrote:
> Is there any built in functionality for iteration that will allow me to 
> detect when I am on the last element?  This would not be hard for an Array, 
> using array.length, but what about a Hash?  How would I know when I am at 
> the last element?

What about a method each_tuple(tuple_length) in Enumerable, that would be kind of a
generalization of each?. This should be O(container.length).

module Enumerable
	def each_tuple(tuple_length)
		tuple = [nil] * tuple_length

		each do |element|
			tuple = tuple[1..-1].push(element)
			yield(tuple)
		end
		(2..tuple_length).each do |i|
			tuple = tuple[1..-1].push(nil)
			yield(tuple)
		end
	end
end

s = ""
[1,2,3,4,5,6,7,8,9,10].each_tuple(2) do |t|
	next unless t[0]
	s << (t[0].to_s + (t[1] ? "," : ""))
end
puts s #gives "1,2,3,4,5,6,7,8,9,10"


[1,2,3,4,5,6,7,8,9,10].each_tuple(2) do |t|
	puts t.inspect
end
#gives:
#[nil, 1]
#[1, 2]
#[2, 3]
#[3, 4]
#[4, 5]
#[5, 6]
#[6, 7]
#[7, 8]
#[8, 9]
#[9, 10]
#[10, nil]

greetings, Florian Pflug