From: Alder Green <alder.green@...>
Date: 2006-05-26T07:03:57+09:00
Subject: Array#delete_if! - a method to delete and return all array items for which the block evaluates to true.

Here's a method to delete and return all items in an Array for which
the block evaluates to true:

class Array
  def delete_if!
    to_delete = []
    to_keep = []
    each do |item|
      (yield item) ? to_delete << item : to_keep << item
    end
    replace(to_keep)
    return to_delete
  end
end

Demonstration:
irb(main):002:0> arr = (1..12).to_a
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
irb(main):003:0> arr.delete_if! {|i| (i % 3) == 0}
[3, 6, 9, 12]
irb(main):004:0> arr
[1, 2, 4, 5, 7, 8, 10, 11]

Would people suggest better implementations?  The obvious problem here
is that we're duplicating arr (to_delete and to_keep contatin together
a cloned arr). I came up with an index based solution to avoid that,
but frankly it was quite ugly.

-- 
-Alder