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Re: Removing equal elements from an array [message #49828 is a reply to message #49761]

Thu, 17 August 2006 10:59

JD Smith
Messages: 850
Registered: December 1999

Senior Member

On Thu, 17 Aug 2006 10:07:59 -0600, R.G. Stockwell wrote:

>
> "Julio" <julio@cpa.unicamp.br> wrote in message
> news:1155653196.084429.65000@74g2000cwt.googlegroups.com...
>> [quoted text muted]
>
> If I follow you correctly, you want to find unique pairs of numbers right?
> How about combining the pairs into one number, and running uniq() on that?
>
> For instance:
>
> A = fltarr(2,4)
> A[0,*]=[20.4, 40.3, 50.2, 50.2]
> A[1,*]=[30.2, 60.2, 32.4, 32.4]
> combo = A[0,*]*1000 + A[1,*]
> indices = UNIQ(combo, SORT(combo))

This method is so deceptively simple that it really seems like it should
work, and sometimes it does, but it doesn't, in general, for floating
point numbers, even if they fall in the proper range. I gave a similar
example before, but it's worth repeating:

[.2,10] => combo=210
[.1,110] => combo=210
[.15,60] => combo=210

or what about:

[5.5,5.5] => combo= 5505.5
[5.2,305.] => combo= 5505.5

The only sure fire way to map a given pair of numbers over a finite range
to a single unique combination, is to scale them to integers, then offset
one set entirely from the other (64bit integers are nice for this). For
small sets of numbers you might not run into this form of collision, but
for many numbers, it's quite likely you would.

JD

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[Message index]

		Removing equal elements from an array By: Julio[1] on Tue, 15 August 2006 07:46
		Re: Removing equal elements from an array By: JD Smith on Thu, 17 August 2006 14:21
		Re: Removing equal elements from an array By: news.qwest.net on Thu, 17 August 2006 13:32
		Re: Removing equal elements from an array By: news.qwest.net on Thu, 17 August 2006 13:06
		Re: Removing equal elements from an array By: JD Smith on Thu, 17 August 2006 10:59
		Re: Removing equal elements from an array By: news.qwest.net on Thu, 17 August 2006 09:07
		Re: Removing equal elements from an array By: Julio[1] on Wed, 16 August 2006 12:42
		Re: Removing equal elements from an array By: R.Bauer on Wed, 13 September 2006 23:32

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