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Re: remove duplicates WITHOUT sorting [message #52564 is a reply to message #52557]

Mon, 12 February 2007 13:15

JD Smith
Messages: 850
Registered: December 1999

Senior Member

On Mon, 12 Feb 2007 09:04:45 -0800, rpertaub@gmail.com wrote:

> Hello All,
> I have an array of 2xn which is a list of coordinates (x,y positions)
> and I need to remove any duplicates in this array. Since they are x,y
> coordinates I cannot really sort the array, hence cannot use the Uniq
> function. Is there another way of doing this?

It's easiest to recast as 1D. HIST_2D (or HIST_ND) does this for you, but
it's easy to do yourself:

index=x + (max(x)+1)*y

and then using UNIQ on this list of indices should give you the row
positions of unique coordinates. HISTOGRAM can work as well (either
with HIST_ND, or by first constructing this index vector above), and
it will be faster, but, as usual, will consume lots of memory (and
potentially be very slow) if your coordinates are sparsely sprinkled over
a large range of values (your current example is somewhat sparse, but not
horrible). UNIQ, with its SORT based implementation, doesn't suffer from
that issue.

JD

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[Message index]

		Re: remove duplicates WITHOUT sorting By: Jean H. on Tue, 13 February 2007 08:10
		Re: remove duplicates WITHOUT sorting By: rpertaub@gmail.com on Tue, 13 February 2007 07:18
		Re: remove duplicates WITHOUT sorting By: JD Smith on Mon, 12 February 2007 13:15
		Re: remove duplicates WITHOUT sorting By: btt on Mon, 12 February 2007 11:23
		Re: remove duplicates WITHOUT sorting By: Brian Larsen on Mon, 12 February 2007 10:38
		Re: remove duplicates WITHOUT sorting By: David Fanning on Mon, 12 February 2007 09:38
		Re: remove duplicates WITHOUT sorting By: Vince Hradil on Mon, 12 February 2007 09:23
		Re: remove duplicates WITHOUT sorting By: Craig Markwardt on Mon, 12 February 2007 09:23
		Re: remove duplicates WITHOUT sorting By: Vince Hradil on Wed, 14 February 2007 07:32

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