From: Jeffrey Schwab <jeff@...>
Date: 2006-10-13T01:00:14+09:00
Subject: Re: Isolating non-unique items in an array

Jeffrey Schwab wrote:
> Jason Burgett 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.
> 
> # Output:
> # ["a", "a", "a", "d", "d"]
> # {"a"=>3, "d"=>2}
> 
> def get_counts(keys)
>     counts = Hash.new(0)
>     keys.each {|k| counts[k] += 1 }
>     counts
> end
> 
> def non_uniq(elements)
>     counts = get_counts(elements)
>     counts.delete_if {|k, v| v < 2 }
>     elements.select {|e| counts.key?(e) }
> end

# Better:
def non_uniq(elements)
     counts = get_counts(elements)
     elements.select {|e| counts[e] > 1 }
end


> 
> elements = ["a", "a", "a", "b", "c", "d", "d"]
> 
> p non_uniq(elements)
> p get_counts(elements).delete_if {|k, v| v < 2 }