Find the number of unique rows and its corresponding index in a matrix
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Hi there, I need to list the unique rows and its corresponding index in a matrix without the using the unique function. I have been suggested to use the unique function but it seems rather time consuming and I have to run many iterations. Any help will be appreciated. Cheers, Vishal
Data:
v1=[1 2 3 4 5; 5 3 3 2 1; 1 2 4 9 7; 1 2 3 4 5; 5 3 3 2 1]
[a,b,c]=unique(v1,'rows','stable')
The required output which I get from the unique function is:
a =
1 2 3 4 5
5 3 3 2 1
1 2 4 9 7
b =
1
2
3
c =
1
2
3
1
2
7 Comments
dpb
on 27 Aug 2013
Edited: dpb
on 27 Aug 2013
Well, it's a big job from scratch every time.
Is this simulation the selection of a subset each time that I seem to recall something about in an earlier posting? If so, I'd suggest the solution may be to do it once for the complete set and the use that and select from it for each randomized sample as well as from the data. That is if the data itself aren't changing, only the sample space.
Jing
on 28 Aug 2013
How long does it take? I don't think UNIQUE will take a lot of time...and my test is running 20 times the UNIQUE line with your v1, the running time is always less than 0.005 seconds.
Accepted Answer
Jan
on 28 Aug 2013
Edited: Jan
on 28 Aug 2013
Perhaps this is more efficient:
v1 = [1 2 3 4 5; 5 3 3 2 1; 1 2 4 9 7; 1 2 3 4 5; 5 3 3 2 1];
vX = v1 * [1, 11, 121, 1331, 14641];
[dummy, b, c] = unique(vX, 'stable');
a = v1(b, :);
unique() has a remarkable overhead, so you could create a local copy of it and remove the not required checks of the inputs etc.
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