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Re: Extract Array positions for a set of Values [message #75427 is a reply to message #75420]

Wed, 09 March 2011 13:29

Gray
Messages: 253
Registered: February 2010

Senior Member

On Mar 9, 5:48 am, Paul Magdon <paulmag...@yahoo.de> wrote:
> Hi,
> have a quite simple problem for which I can find a fas solution:
>
> 1.) I have an IntArray A (e.g a result from LABEL_REGION)
>
> 1 1 1 1 0 0 0
> 1 1 1 1 0 0 2
> 0 0 0 0 9 0 2
>
> 2.) I have a vector B with Integers (e.g. 1,2,9)
>
> Now I want to extract the positions of B in A and set all values in A which are included in B to let's say 99. How can I do this without a loop?
> I tested HISTOGRAM(,REVERSE_INDICES) but as B is not consecutive (e.g 1,2,3,4) I can't find a solution.
>
> Cheers Paul

Here's a solution that uses a FOR-loop and histogram:

H = histogram(A,min=0,max=max(B),reverse_indices=ri)
for i=0,n_elements(B)-1 do begin
if H[B[i]] eq 0 then continue
A[ri[ri[B[i]]:ri[B[i]+1]-1]] = 99
endfor

Who cares if B isn't consecutive? Just use it to index the histogram
(and the reverse_indices array), so you only have to loop over B. I
would remove duplicate values, if any, from B beforehand to save
redundant iterations.

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[Message index]

		Re: Extract Array positions for a set of Values By: wlandsman on Thu, 10 March 2011 06:54
		Re: Extract Array positions for a set of Values By: Jeremy Bailin on Thu, 10 March 2011 05:49
		Re: Extract Array positions for a set of Values By: Gray on Wed, 09 March 2011 13:29
		Re: Extract Array positions for a set of Values By: Jeremy Bailin on Wed, 09 March 2011 06:37
		Re: Extract Array positions for a set of Values By: wlandsman on Wed, 09 March 2011 03:08

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