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MathGroup Archive 2005

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Re: SameTest in Union

  • To: mathgroup at smc.vnet.net
  • Subject: [mg61140] Re: [mg61106] SameTest in Union
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Tue, 11 Oct 2005 03:21:13 -0400 (EDT)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

lst={1.1101,1.11095,1.11076,1.09,2.3523,2.352,2.35211};

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

{1.09,1.1101,2.352}

Union[lst,SameTest->(Abs[#1-#2]<9*^-1&)]

{1.09,2.352}


Bob Hanlon

> 
> From: Jack Goldberg <jackgoldberg at comcast.net>
To: mathgroup at smc.vnet.net
> Date: 2005/10/10 Mon AM 02:40:08 EDT
> Subject: [mg61140] [mg61106] SameTest in Union
> 
> 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
> 
> 


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