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MathGroup Archive 2005

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Re: SameTest in Union

  • To: mathgroup at smc.vnet.net
  • Subject: [mg61110] Re: [mg61106] SameTest in Union
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Tue, 11 Oct 2005 03:20:04 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 10 Oct 2005, at 15:40, Jack Goldberg wrote:

> Hi Folks,
>
> I know there is a simple answer to this question but the help index
> idoes not help!
>
> I have a list, something like this:
>
> lst = {1.1101, 1.11095, 1.11076, 1.09, 2.3523, 2.352. 2.35211}
>
> I want to remove from the list those entries which are near each
> other but not identical, leaving only one representative for each of
> these numbers.  One approach is to use  Union with the option
> SameTest->???.   Here the same test might be that the difference
> between entries is less than, say 10^(-2).   But I can't seem to get
> SameTest to work.  So, what I want is
>
> Union[ lst, SameTest- > ?]
>
> so that  the union returns
>
> {1.1101,  2.35211}
>
> Here, I chose 2 representatives.  Any other choice is OK;   say,
>
> {1.11095,  2.352}
>
> is also satisfactory.
>
> There may be other ways to do this, but I thought of  Union  first.
> Perhaps, Cases  or Select  might be better.  Any help is appreciated.
>
> Jack
>
>

The problem could be that your list has no comma between the last two  
entries.

In[28]:=
lst = {1.1101, 1.11095, 1.11076, 1.09, 2.3523, 2.352,
     2.35211};

In[29]:=
Union[lst, SameTest -> (Abs[#1 - #2] < 10^(-2) & )]

Out[29]=
{1.09, 1.1101, 2.352}

Seems to wok fine?

Andrzej Kozlowski


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