From: "David A. Black" <dblack@...>
Date: 2009-07-18T10:14:01+09:00
Subject: Re: [Q] removing array duplicates where a subset is unique

Hi --

On Sat, 18 Jul 2009, brabuhr@gmail.com wrote:

> On Fri, Jul 17, 2009 at 7:51 PM, Chuck Remes<cremes.devlist@mac.com> wrote:
>> (And Joel, I have presorted the array prior to removing the
>> dupes so I have already taken care of the ordering issue.)
>
> I think what Joel was referring to was that in Ruby 1.8 a Hash doesn't
> maintain insertion order when traversed (Ruby 1.9 does maintain
> insertion order):
>
> ruby 1.8.2 (2004-12-25) [powerpc-darwin8.0]:
> irb(main):001:0> h = {}
> => {}
> irb(main):002:0> 5.times{|n| h[n] = n}
> => 5
> irb(main):003:0> h
> => {0=>0, 1=>1, 2=>2, 3=>3, 4=>4}
> irb(main):004:0> h["sadf"] = 3
> => 3
> irb(main):005:0> h
> => {0=>0, 1=>1, "sadf"=>3, 2=>2, 3=>3, 4=>4}

If you wanted to maintain order you could (for some but probably not
much performance penalty) do something like:

   def dedup(ary)
     uniq = {}
     res = []
     ary.each do |line|
       key = line[0..2]
       next if uniq[key]
       res << (uniq[key] = line)
     end
     res
   end


David

-- 
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