From: Thomas Chust <chust@...>
Date: 2009-07-28T04:10:53+09:00
Subject: Re: Set class and repetetive elements

2009/7/27 Jos Backus <jos@catnook.com>:
> On Tue, Jul 28, 2009 at 03:21:38AM +0900, Marcin Grski wrote:
>> It would be nice to have for example {5, 1, 1, 1} in Set class object.
>> Is it possible? Which method should I use to add element in that way?
>
> Sounds like you want a Bag, not a Set. I don't know of aany implementation but
> it's probably not hard to create one - all you have to do is keep track of the
> count of each element.

What about using a Hash mapping objects to counts? That way you can
still do efficient lookups whether something is contained in the Bag.

A simple implementation could look like this:

  class Bag < Hash
    def initialize(*contents)
      super 0
      contents.each {|item|
        self[item] += 1
      }
    end

    def each
      return enum_for(__method__) unless block_given?

      each_pair {|item, count|
        count.times { yield item }
      }
    end

    def to_a
      each.to_a
    end
  end

cu,
Thomas


-- 
When C++ is your hammer, every problem looks like your thumb.