From: William James <w_a_x_man@...>
Date: 2006-02-05T20:28:19+09:00
Subject: Re: Quiz #65, Principle of Great Surprise, and Array.delete sledgehammer

Dave Howell wrote:
> I thought I was actually going to enter my first RubyQuiz, but I've
> spent three times as much time trying to get Ruby to stop surprising me
> as I have trying to implement my algorithm, and I've had to abandon my
> effort since I don't have the time to spend. Sigh.
>
> Can somebody explain to me how I'm supposed to delete a *single*
> element from an array based on equivalence with an object? and get back
> said array with said element deleted?
>
> In other words....
>
> ar = [1, 2, 3, 8, 15, 15, 8]
>
> ar.delete_one_element!(15)
> => [1, 2, 3, 8, 15, 8]
>
> ar.delete_one_element!(14)
> => [1, 2, 3, 8, 15, 15, 8]
>
> ar.delete_one_element!(nil)
> => [1, 2, 3, 8, 15, 15, 8]
>
> I did find so many different ways of not doing this....
>
> Too enthusiastic....
> ar.delete(15)
> => 15
> ar
> => [1, 2, 3, 8, 8]
>
> Right results, wrong output...
> ar.slice!(ar.index(15))
> => 15
> ar
> => [1, 2, 3, 8, 15, 8]
>
> and also surprised me by not handling 'nil' as I wanted...
> ar.slice!(ar.index(13))
> TypeError: no implicit conversion from nil to integer
>          from (irb):8:in `slice!'
>          from (irb):8
>
>
> I mean, this seems so, er, obvious! "Please find one instance of this
> object in the array, and return to me the array without that object. If
> the array doesn't have that object, then just give the array back to
> me."

This may not be of any use to you, but here's a way to delete all
elements but the first:

class Array
  def no_dup!( x )
    (i = index(x)) && delete( x ) && insert(i,x)
    self
  end
end

And here's another version of delete_one_element!.

class Array
  def delete_one_element!( x )
    (i = index(x)) && delete_at( i )
    self
  end
end