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Re: How to get matching elements of array efficiently [message #69932 is a reply to message #69928]

Tue, 23 February 2010 13:06

wlandsman
Messages: 743
Registered: June 2000

Senior Member

You might look at Craig Markwardt's program match2 in
http://idlastro.gsfc.nasa.gov/ftp/pro/misc/match2.pro

For your example, one would type
IDL> match2, a, b, suba, subb
IDL> print,where(suba GE 0)
0 2 3 4

You might be able to make match2.pro more efficient, because it also
gives the index of a (not necessarily unique) value in B that matches
a value in A, which is information you don't need. --Wayne

On Feb 23, 3:11 pm, JJ <j...@cornell.edu> wrote:
> Hi All,
>
> I'm looking for an efficient (non-loop) solution to this problem. I
> have two arrays A, B. The elements of A are not necessarily unique,
> nor is A necessarily sorted. I'd like to find all the indices in A
> that match values that occur in B.
>
> For example, if A = [7,1,8,7,8], B = [7,8], the result should be
> [0,2,3,4].
>
> A and B can have many (order millions) of unique values, so I'd rather
> avoid a loop if I can.
>
> Is there any way to do this efficiently?
>
> Thanks.
>
> -JJ

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[Message index]

		Re: How to get matching elements of array efficiently By: JJ on Mon, 01 March 2010 11:18
		Re: How to get matching elements of array efficiently By: JJ on Mon, 01 March 2010 10:58
		Re: How to get matching elements of array efficiently By: JDS on Wed, 24 February 2010 14:26
		Re: How to get matching elements of array efficiently By: Jeremy Bailin on Wed, 24 February 2010 06:46
		Re: How to get matching elements of array efficiently By: rogass on Wed, 24 February 2010 00:54
		Re: How to get matching elements of array efficiently By: wlandsman on Tue, 23 February 2010 13:06
		Re: How to get matching elements of array efficiently By: penteado on Tue, 23 February 2010 12:36

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