From: nobu.nokada@...
Date: 2002-02-11T19:06:51+09:00
Subject: Re: array diff

Hi,

At Mon, 11 Feb 2002 18:17:21 +0900,
Tobias Reif <tobiasreif@pinkjuice.com> wrote:
> I need to get the difference of two arrays; more precisely, the rest of 
> their intersection.
(snip)
> But here,
> 
> [1,1,1] - [1,1]
> -> []
> 
> I need to get [1].

Array#- actually treats arrays as Sets.

class Array
  def diff(a)
    ary = dup
    a.each {|i| ary.delete_at(i) if i = ary.index(i)}
    ary
  end
end

p [1,2,3].diff [3,1]		# => [2]
p [1,2,3,3].diff [3,3,1]	# => [2]
p [1,1,1].diff [1,1]		# => [1]

-- 
Nobu Nakada