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Collapsing integer data into consecutive integers?

Asked by Mark on 18 Jun 2013

I have a matrix of values that include integers >= 0. There are repeats, and also gaps in consecutiveness. I would like to collapse the data into consecutive integers, keeping the order intact.

Example: [ 0 1 4 4 1 5 8 1 4]

would go to

[ 0 1 2 2 1 3 4 1 2]

I can do this with loops and brute force, but I'm wondering if there's any quick way to do this since it is frequently called within a loop?

Thanks!

3 Comments

John on 18 Jun 2013

I don't understand what you're aiming for... the example result you show isn't consecutive (1 to 3? 4 to 1?), and you're entirely changing some of the numbers.

John on 18 Jun 2013

It looks like you just divided everything by 2, rounding up.

Mark on 18 Jun 2013

Not consecutive in the array, but consecutive in the counting of unique numbers in the original. I.e., there are 5 unique numbers in the original vector, 0 1 4 5 and 8. I wanted to map those to 0 1 2 3 4. (The divide by two and round was just coincidence!) The problem has been solved below. Thanks.

Mark

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2 Answers

Answer by Tom on 18 Jun 2013
Accepted answer
[~,~,I] = unique([ 0 1 4 4 1 5 8 1 4]);
disp(I-1)

0 Comments

Tom
Answer by Iain on 18 Jun 2013
 Ex = [ 0 1 4 4 1 5 8 1 4]; % A row
 V = unique(Ex); % should be a row 
 L = bsxfun(@eq,Ex,V); 
 Collapsed = [0:(numel(V)-1)]*L;
 Reconstructed = V' * L;

1 Comment

Mark on 18 Jun 2013

Thanks to both.

Iain

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