the first time there is zero before and after a particular index

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Masih Alavy
Masih Alavy 2017-7-30
回答： Image Analyst 2017-7-30
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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采纳的回答

the cyclist
the cyclist 2017-7-30
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))

更多回答（1 个）

Image Analyst
Image Analyst 2017-7-30
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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