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Re: IDL sorting [message #56343]

Thu, 18 October 2007 14:58

Karl Schultz
Messages: 341
Registered: October 1999

Senior Member

wlandsman <wlandsman@gmail.com> wrote:
> On Oct 18, 2:30 pm, Karl Schultz <k...@io.frii.com> wrote:
>> Because it is not a *stable* sort. Stable sorting algorithms preserve
>> the order of equal keys.
>>
>>> 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.
>>
>> Are you using this SORT function from the command line? If so, you
>> are using a shell function or a sort program in your PATH. Someone
>> probably decided that a stable sort made more sense for people sorting
>> things from the command line or from shell scripts. Reasonable.
>>
>
> I don't understand this paragraph. I am just using the IDL intrinisc
> SORT command. On every Linux box I have ever been on, it appears
> that the C lib sort algorithm used by IDL SORT() *is* stable, whereas
> it is *not* stable on Windows or MacOS.
>

When you said "SORT function on Linux boxes", I thought you meant from the
Linux command line. My bad.

So it looks like the qsort() implementation on the Linux distros you tried
happens to be stable. That's all.

--
Karl Schultz kws@frii.com
There are 844,739 ways to enjoy a Waffle House hamburger.

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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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