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Re: IDL sorting [message #56353 is a reply to message #56347]

Thu, 18 October 2007 08:50

wlandsman
Messages: 743
Registered: June 2000

Senior Member

On Oct 18, 8:20 am, Wox <nom...@hotmail.com> wrote:

> Sorting the resulting 64-bit longs would do the trick, wouldn't it?
>
> function sort,array
> array64=ishft(long64(array),32)+lindgen(n_elements(array))
> return,sort(array64)
> end

That is clever. My tests on my V6.4 Linux box find that it is
usually faster than bsort.pro. It is somewhat slower when there are
only a few duplicate values

> Btw, I didn't want to ask this, but
> why is IDL's sort doing this?

IDL just uses the sort algorithm of the underlying OS. As far as I
am aware, the SORT function on Linux boxes *does* preserve the order
of equal values, but that on Mac and Windows machines does not. I
would be interested to hear if anyone finds any exceptions to this
rule.

> Is there any situation where mixing up
> the order of equal values has a benefit?

None that I can think of. But if you just want the fastest SORT
possible, you might not care what happens to the equal values.

Actually, I think a good suggestion to ITTVIS would be to add a /
preserve_equal keyword or something similar to SORT(). This topic
comes up repeatedly.

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[Message index]

		Re: IDL sorting By: Karl Schultz on Thu, 18 October 2007 14:58
		Re: IDL sorting By: wlandsman on Thu, 18 October 2007 13:43
		Re: IDL sorting By: Karl Schultz on Thu, 18 October 2007 11:30
		Re: IDL sorting By: wlandsman on Thu, 18 October 2007 08:50
		Re: IDL sorting By: Wox on Thu, 18 October 2007 05:20
		Re: IDL sorting By: Loren Anderson on Wed, 17 October 2007 14:15
		Re: IDL sorting By: David Fanning on Wed, 17 October 2007 08:38
		Re: IDL sorting By: Loren Anderson on Wed, 17 October 2007 08:37
		Re: IDL sorting By: JD Smith on Thu, 01 November 2007 17:02

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