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Re: fast array comparison [message #33151 is a reply to message #33150]

Mon, 09 December 2002 07:25

JD Smith
Messages: 850
Registered: December 1999

Senior Member

On Sun, 08 Dec 2002 18:39:23 -0700, Craig Markwardt wrote:

> "Sean Raffuse" <sean@me.wustl.edu> writes:
>> David,
>>
>> Thanks for this. It works almost perfectly. I am a little confused
>> though. It seems that the indices keyword returns the indices of the
>> requested array and not the available array.
>
> Greetings Sean--
>
> Another option is CMSET_OP from my web page. It uses the HISTOGRAM
> technique, if the dynamic range of values is small, but graduates to a
> different, sort/uniq-based method, if the dynamic range is large.
> Indices can be returned using the /INDEX keyword. [ In case it isn't
> obvious, you want to use the 'AND' operation. ]
>
> CMSET_OP also returns indices from the *first* array. This is not a
> problem for your application, since you can simply swap the positions of
> the first and second arrays in the function call.
>
> Yours,
> Craig
>
> http://cow.physics.wisc.edu/~craigm/idl/idl.html (under Array/Set Ops)

This topic was discussed ad naseum over the past couple of years, with
the critical differences between looking for the values and looking for
the indices of intersection pointed out. Several different methods were
compared using HISTOGRAM, SORT, and direct array inflation. Depending on
your problem size, one of these will be fastest. Usually. ;).

Give it a search on Gusenet.

JD

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[Message index]

		Re: fast array comparison By: JD Smith on Mon, 09 December 2002 09:59
		Re: fast array comparison By: David Fanning on Mon, 09 December 2002 08:07
		Re: fast array comparison By: David Fanning on Mon, 09 December 2002 08:00
		Re: fast array comparison By: Sean Raffuse on Mon, 09 December 2002 07:48
		Re: fast array comparison By: JD Smith on Mon, 09 December 2002 07:25
		Re: fast array comparison By: Sean Raffuse on Mon, 09 December 2002 07:24
		Re: fast array comparison By: Craig Markwardt on Sun, 08 December 2002 17:39
		Re: fast array comparison By: David Fanning on Sun, 08 December 2002 12:47
		Re: fast array comparison By: David Fanning on Sun, 08 December 2002 12:40
		Re: fast array comparison By: Sean Raffuse on Sun, 08 December 2002 12:35
		Re: fast array comparison By: Sean Raffuse on Sun, 08 December 2002 12:32
		Re: fast array comparison By: David Fanning on Sun, 08 December 2002 09:45

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