the first time there is zero before and after a particular index
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Masih Alavy
il 30 Lug 2017
Risposto: Image Analyst
il 30 Lug 2017
Hi All, I have a matrix which looks like this:
1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 Let's say that I want to find out at what indices there is the first zero happening before and after index 20. How do we do this? So, in my example here, my points of interest will be: 7 (for before) and 37 (for after).
Thanks
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the cyclist
il 30 Lug 2017
Here is one straightforward way:
x = [1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0];
anchor = 20;
positionIndex = 1:numel(x);
lastPriorZero = max(find(x==0 & positionIndex<anchor))
firstLaterZero = min(find(x==0 & positionIndex>anchor))
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Image Analyst
il 30 Lug 2017
If you want to find the 0's just outside the 1's, and you have the Image Processing Toolbox, you can do this:
x = [1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0]
dilatedx = imdilate(x, [1,1,1]) % Grow 1 regions outward
indexes = find(dilatedx ~= x) % Find locations of mismatches.
and you get
indexes =
4 7 37
as you should.
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