From: Joel VanderWerf <vjoel@...>
Date: 2009-07-18T07:35:28+09:00
Subject: Re: [Q] removing array duplicates where a subset is unique

Chuck Remes wrote:
> I need to remove duplicates from an array of arrays. I can't use 
> Array#uniq because some fields are different and not part of the "key." 
> Here's an example where the first 3 elements of each sub array are the 
> "key" and determine uniqueness. I want to keep only the first one I get.
> 
>  >> a = [[1, 2, 3, 4, 5], [1, 2, 3, 9, 4], [1, 2, 3, 4, 4]]
> => [[1, 2, 3, 4, 5], [1, 2, 3, 9, 4], [1, 2, 3, 4, 4]]
> 
> The return value of deduplicating this array should be: [[1, 2, 3, 4, 5]]

Might be faster if your intermediate is a hash, so instead of N**2 time 
it's N.

a = [[1, 2, 3, 4, 5], [1, 2, 3, 9, 4], [1, 2, 3, 4, 4]]

h = {}
a.each do |row|
   h[row[0..2]] ||= row # record the first match
end

p h.values # ==> [[1, 2, 3, 4, 5]]


Note that the output may come out in a different order. Does that matter?

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407