From: "David A. Black" <dblack@...>
Date: 2008-10-13T01:03:33+09:00
Subject: Re: Compare Arrays

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Hi --

On Sun, 12 Oct 2008, R=FCdiger Brahns wrote:

> Todd Benson schrieb:
>> On Sat, Oct 11, 2008 at 10:50 PM, Tj Superfly <nonstickglue@verizon.net>=
=20
>> wrote:
>>> Hey, I just have a quick question about arrays.
>>>=20
>>> I have two different ones that I would like to compare.
>>>=20
>>> Example:
>>>=20
>>> Array 1: cats, dogs, monkeys
>>>=20
>>> Array 2: cats, fish, dogs, birds, monkeys
>>>=20
>>> Now, I would like to compare array 2 with array 1 and have it spit out
>>> any words that aren't in both... if that makes sense.
>>>=20
>>> So what the program should output is fish, monkeys.
>>=20
>> Hmm.  I'm assuming you are looking for ["fish", "birds"], and if you
>> are, do union, then subtract intersection...
>>=20
>> a =3D %w( cats dogs monkeys )
>> b =3D %w( cats fish dogs birds monkeys )
>>=20
>> (a | b) - (a & b)
>
> Why not just
>
> b - a

As Brian C. said, that works but only if b is always a superset of a.
If not, you get:

   [1,2,3] - [2,3,4]   # [1], should be [1,4]

> ? But as I understand him what he wants is
>
> a & b

I think he wants:

   a ^ b  # exclusive or

which unfortunately doesn't exist :-) It's basically

   (a | b) - (a & b)

which I think someone else posted. Or, if you don't want to create
that many intermediate arrays, you could do:

module EnumExOr
   def ^(other)
     reject {|e| other.include?(e) }.
     concat(other.reject {|e| include?(e) })
   end
end

array =3D [1,2,3,4,5].extend(EnumExOr)

p array ^ [3,4,5,6,7]   # [1,2,6,7]


David

--=20
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