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MathGroup Archive 1998

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Re: Union[{0},{0.}] = {0,0.}?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg12719] Re: [mg12662] Union[{0},{0.}] = {0,0.}?
  • From: "Tomas Gargz" <tgarza at mail.internet.com.mx>
  • Date: Wed, 3 Jun 1998 02:21:08 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Chris Farr wrote:

>Union[{0},{0.}] ÿ0,0.}.
>Why?
>I would like the above to return only {0}.
>The root of the problem is that Mathematica thinks they are the same:
>SameQ[{0},{0.}] ÿalse
>How can I get around this?  The following doesn't help either.
>Union[{ N[0] },{0.}] ÿ0,0.}
>Any ides out there?

Chris:
For one thing, 0 and 0. are distinct elements, so Mathematica is giving
ÿhe right answer.
In[1]:ÿead[0]
Out[1]ÿnteger
In[2]:ÿead[0.]
Out[2]ÿeal

Now. N[0] will not give 0. as you might like it to. It produces a real,
ÿowever, for any nonzero number.  You could get round the problem by
ÿransforming every real 0. to an integer 0 in the list you are
operating ÿpon with Union (or viceversa).

If your list is b, say,

In[3]:ûÿ0},{0.}};

then

In[4]:ÿ
Union[b/.{x_}->If[xð.,ToExpression[StringTake[ToString[0.], 1]]]]
Out[4]ÿ0}

I hope I did understand your problem.

Tomas Garza
Mexico City 


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