From: Alex Young <alex@...>
Date: 2006-10-13T00:52:19+09:00
Subject: Re: Isolating non-unique items in an array

Tim Pease wrote:
> On 10/12/06, Jason Burgett <jasbur@gmail.com> wrote:
>> I'm basically trying to the opposite of .uniq Let's say I have an array:
>>
>> ["a", "a", "a", "b", "c", "d", "d"]
>>
>> I would like to boil this down by first tossing the values that only
>> appear once. Which leaves me with:
>>
>> ["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.
>>
>> -- 
>> Posted via http://www.ruby-forum.com/.
>>
>>
> 
> class Array
>  def count( item )
>    return 0 unless self.include? item
> 
>    c = 0
>    self.each {|i| c += 1 if i == item}
>    return c
>  end
> end
> 
> ary = %w(a a a b c d d)
> new_ary = ary.select {|item| ary.count(item) > 1}
> 

Better:

class Array
   def counts # could be golfed, but clarity is king
     result = Hash.new{0}
     self.each {|a| result[a] += 1}
     result
   end
end

a = ["a", "a", "a", "b", "c", "d", "d"]
c = a.counts
a.reject{|b| c[b] == 1} # => ["a", "a", "a", "d", "d"]

-- 
Alex