From: r2d2@... (Niklas Frykholm)
Date: 2001-01-18T22:10:02+09:00
Subject: [ruby-talk:9504] Re: array.each_index_but_last ?

>What is the idiomatic Ruby way to go through all the elements of an array,
>except the last one, gettting the index?
>...
>seems less than neat.
>
>Reason I want to do this -- If one is producing a difference table from an
>array such that: 
>    d[i] = a[i+1] - a[i]

If you want to do things like this a lot you could create iterators for
looping over the array elements pairwise

class Array
	def each_pair
		(0...size-1).each {|i| yield(self[i],self[i+1])}
	end
	def each_pair_with_index
		(0...size-1).each {|i| yield(self[i],self[i+1],i)}
	end
end

Now you could just do

d = []
a.each_pair {|i, j| d.push(j-i)}

// Niklas