Re: the Union of real numbers
- To: mathgroup at smc.vnet.net
- Subject: [mg7198] Re: [mg7004] the Union of real numbers
- From: "caffa" <caffa at iabg.de>
- Date: Fri, 16 May 1997 02:30:26 -0400 (EDT)
- Organization: iabg.de
- Sender: owner-wri-mathgroup at wolfram.com
Russell Towle wrote:
> I am trying to apply the Union function to a list of real numbers,
> in which many duplicates occur. However, small differences between
> the numbers cause some of the duplicates to be retained instead of
> discarded.
>
> Suppose the list of real numbers is called k, my present work-around
> is as follows:
>
> Union [ Rationalize [ k, 10^-6 ] ].
>
> This does discard the duplicates. Is there a better method?
Yes. Try:
In[1]:= lst = {3.0, 2.001, 2.0, 1.01, 1.02};
In[2]:= eps = 0.02;
In[3]:= Union[lst, SameTest->(Abs[#1-#2]<=eps &)]
Out[3]= {1.01, 2., 3.}
Compare:
In[4]:= Union[Rationalize[lst, 0.02]]
51
Out[4]= {1, --, 2, 3}
50
Vittorio G. Caffa
Vittorio Caffa
IABG, Abt. CC22
Einsteinstr. 20
D-85521 Ottobrunn
Tel.: (089) 6088-2054
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eMail: caffa at iabg.de