From: ara.t.howard@...
Date: 2006-10-13T05:53:27+09:00
Subject: Re: Isolating non-unique items in an array

On Fri, 13 Oct 2006, Phrogz wrote:

> WATANABE Hirofumi wrote:
>> Jason Burgett <jasbur@gmail.com> writes:
>>> ["a", "a", "a", "d", "d"]
>>>
>>> Then I need to somehow determine that "a" appears 3 times and "d"
>>> appears 2 times. Any help would be great. Thanks.
>>
>> % irb
>>>> a = ["a", "a", "a", "b", "c", "d", "d"]
>> => ["a", "a", "a", "b", "c", "d", "d"]
>>>> a.select{|i| a.grep(i).size > 1}
>> => ["a", "a", "a", "d", "d"]
>
> Taking that one step further to meet his second need:
>
> class Array
>  def duplicates_count
>    uniq.map{ |e|
>      if ( count = grep(e).size ) > 1
>        { e => count }
>      end
>    }.compact
>  end
> end
>
> a = ["a", "a", "a", "b", "c", "d", "d"]
> p a.duplicates_count
> #=> [{"a"=>3}, {"d"=>2}]

that's O(n^2) though... the others are O(n)

-a
-- 
my religion is very simple.  my religion is kindness. -- the dalai lama