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Re: The intersection of 2 arrays [message #8432 is a reply to message #8357]

Tue, 04 March 1997 00:00

wonko
Messages: 22
Registered: March 1997

Junior Member

williams@irc.chmcc.org (Phil Williams) wrote:

> I know that I can find the union of two arrays by doing something like
>
> temp = [array1, array2]
> union = temp(uniq(temp, sort(temp)))
>
> But how would I go about finding the intersection of the two arrays?
> i.e. Is there a nice vector way of doing it rather than brute force?
> (aka: Which IDL function did I miss this time?)

How big are your elements?

My idea would be something like this:

mask = bytarr( max( [ array1, array2 ] ) + 1 )
mask(array1) = 1b
mask(array2) = mask(array2) + 1b
intersection = where( mask eq 2b, count )

Works for positive values only. And the intersection of [ 1L, 2L ] and [
1L, 100000000L ] might be a problem...

Alex
--
Alex Schuster Wonko@weird.cologne.de
alex@pet.mpin-koeln.mpg.de

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[Message index]

		The intersection of 2 arrays By: Phil Williams on Mon, 03 March 1997 00:00
		Re: The intersection of 2 arrays By: James Tappin on Thu, 06 March 1997 00:00
		Re: The intersection of 2 arrays By: wonko on Tue, 04 March 1997 00:00
		Re: The intersection of 2 arrays By: J.D. Smith on Tue, 04 March 1997 00:00
		Re: The intersection of 2 arrays By: Marty Ryba on Tue, 04 March 1997 00:00

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