Get the numbers of rows where values change

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Hi,
I have an array of data, structured like this:
Latitude Longitude Height
23 54 7
23 54 3
23 54 8
23 55 4
23 55 2
24 54 0
24 54 1
24 55 2
24 55 7
How can I get the numbers of the rows where either Latitude or Longitude changes (so from the example above the output would be rows 3, 5 and 7)?
  2 Comments
Maja Zdulska
Maja Zdulska on 16 Jul 2020
Yes, sorry, you're absolutely correct.

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Accepted Answer

Image Analyst
Image Analyst on 16 Jul 2020
By the time you get down to row 3, nothing has changed yet. Row 3 is still the same as rows 1 and 2. Don't you mean 4, 6, and 8? Those are the actual rows where a change is first encountered.
Try this:
m = [
23 54 7
23 54 3
23 54 8
23 55 4
23 55 2
24 54 0
24 54 1
24 55 2
24 55 7]
latChanged = [0; diff(m(:, 1))] % Logical -- use find() if you want row numbers.
lonChanged = [0; diff(m(:, 2))] % Logical -- use find() if you want row numbers.
eitherChanged = find(latChanged | lonChanged) % Row numbers where either lat OR lon changed.

More Answers (1)

David Hill
David Hill on 16 Jul 2020
b=diff(a);%a being your matrix
c=find(b(:,1)~=0|b(:,2)~=0);%c=3,5,7

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