From: Adam Shelly <adam.shelly@...>
Date: 2006-02-05T13:53:18+09:00
Subject: Re: Quiz #65, Principle of Great Surprise, and Array.delete sledgehammer

On 2/4/06, Dave Howell <groups@grandfenwick.net> wrote:
>
>  ... . The "-" operator also was
> massively destructive, removing all duplicates when used.

I ran into that problem too when I was coding the quiz.
Does anyone else find it strange that a + b - b != a  if a contains
duplicates of any element in b?

To finish the quiz, I added this method:

class Array
  def subtract arr
    return clear if arr==self
    arr.each{|e| if (n=index(e)) then delete_at(n); end }
    self
  end
end

a = [1,2,3,3,3,4,5,5,6]
=> [1, 2, 3, 3, 3, 4, 5, 5, 6]

b = [3,4,5]
=> [3, 4, 5]

a.subtract b
=> [1, 2, 3, 3, 5, 6]

a
=> [1, 2, 3, 3, 5, 6]


-Adam