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Re: Array comparison part 2 [message #32380]

Fri, 04 October 2002 13:04

JD Smith
Messages: 850
Registered: December 1999

Senior Member

On Thu, 03 Oct 2002 09:33:24 -0700, Dick Jackson wrote:

> "Sean Raffuse" <sean@me.wustl.edu> wrote in message
> news:anhkqb$ipf$1@newsreader.wustl.edu...
>> Thanks for all the help on my first question. I now have a related
>> question.
>>
>> What is the best (read: fastest) way to do the following:
>>
>> I have an array of coordinates, A = intarr(2,25) and I have another
>> array of a specific location, B = [125,1043]
>>
>> I would like to determine if location B is one of the coordinates in
> A. I
>> need to know if A[*,?] = 125, 1043
>>
>> Is it possible to do this without splitting A?
>
> Oh, sure. Using the "replicate data rather than loop" principle, we
> stretch B to be the same shape as A, then compare. Try this:
>
> nCoords=25
> a=indgen(2,nCoords)
> b=[4,5]
> print,Total(Total(a EQ (Rebin(b, 2, nCoords)), 1) EQ 2) GT 0
>
> (result is 1, there is a match)
>
> b=[4,6]
> print,Total(Total(a EQ (Rebin(b, 2, nCoords)), 1) EQ 2) GT 0
>
> (result is 0, there is no match)
>
> To find *which* one(s) it matches, look at the inner part: Total(a EQ
> (Rebin(b, 2, nCoords)), 1) EQ 2
>
> This will be 1 where 'a' matches a pair of 'b' entries, use Where to
> find which one (or more) it matches.

A faster way to do this, if you don't care about the locations where
equality occurs, is to use array_equal(), which halts as soon as it find
an equal value:

print, array_equal(a[0,*] ne b[0] OR a[1,*] ne b[1],1b) eq 0b

JD

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[Message index]

		Re: Array comparison part 2 By: JD Smith on Fri, 04 October 2002 13:04
		Re: Array comparison part 2 By: tam on Fri, 04 October 2002 10:21
		Re: Array comparison part 2 By: Dick Jackson on Fri, 04 October 2002 08:46
		Re: Array comparison part 2 By: James Kuyper on Fri, 04 October 2002 07:20
		Re: Array comparison part 2 By: tam on Fri, 04 October 2002 06:58
		Re: Array comparison part 2 By: chia on Thu, 03 October 2002 17:27
		Re: Array comparison part 2 By: Dick Jackson on Thu, 03 October 2002 09:33

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