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Re: Intersection of 2 sets--Beginner IDL question [message #27283 is a reply to message #27281]

Wed, 17 October 2001 06:58

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

John-David Smith (jdsmith@astro.cornell.edu) writes:

> It's amazing how much recycled information flows through the newsgroup, if you
> watch it long enough. I remember just like it was 4 years ago the detailed
> discussions with which we whiled away our days, concerning value-based
> intersection vs index-based intersection, order N vs. unknown order operations,
> etc.
>
> I do, however, still cringe when I read on that page of yours:
>
> "These routines are faster than previously published functions, e.g. Contain..."
>
> since I whipped up contain() to prevent the problem of an operation scaling out
> of control on sparse data sets (as set_intersection does -- a feature they warn
> you of). You can read all about a variety of intersection methods if you like:
>
> http://groups.google.com/groups?selm=38CBF8B6.5BF0AB50%40ast ro.cornell.edu
>
> In a classic example posed by Mark Fardal, you are matching up social security
> numbers in two lists containing age and income. The set_intersection style
> solution fails miserably here, and to a lesser degree for any arrays which are
> somewhat sparse (where *somewhat* seems to be about 1 in 10, depending on lots
> of factors).
>
> Ah, the glory days.

Alright, alright. I'm spending the day updating my web
page. :-(

Cheers,

David

--
David W. Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		Re: Intersection of 2 sets--Beginner IDL question By: John-David T. Smith on Wed, 17 October 2001 09:51
		Re: Intersection of 2 sets--Beginner IDL question By: Craig Markwardt on Wed, 17 October 2001 08:05
		Re: Intersection of 2 sets--Beginner IDL question By: David Fanning on Wed, 17 October 2001 06:58
		Re: Intersection of 2 sets--Beginner IDL question By: R.Bauer on Tue, 16 October 2001 23:58
		Re: Intersection of 2 sets--Beginner IDL question By: John-David T. Smith on Tue, 16 October 2001 22:00
		Re: Intersection of 2 sets--Beginner IDL question By: David Fanning on Tue, 16 October 2001 20:52
		Re: Intersection of 2 sets--Beginner IDL question By: Mark Hadfield on Tue, 16 October 2001 20:37
		Re: Intersection of 2 sets--Beginner IDL question By: David Fanning on Tue, 16 October 2001 20:01
		Re: Intersection of 2 sets--Beginner IDL question By: Craig Markwardt on Wed, 17 October 2001 14:49

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