How to detect isolated points in a vector

Question

CSCh 2023-9-21

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2024082-how-to-detect-isolated-points-in-a-vector

评论： CSCh 2023-9-22

Hi,

I have a vector (see attachment), and I would like to detect isolated points (marked with red cicles in the image). Isolated in that sense, that same values have a certain distance to these. I would need the indices.

Thank you

Chris

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CSCh 2023-9-21

Dear Joshi, thanks for your answer. please have a kook to the provided example, in the attachment.

Dyuman Joshi 2023-9-21

I have seen the image. It does not do a good job of explaining what you mean by "isolated points".

That is why I asked for more information.

Provide a mathematical explaination of the criteria to use to determine which points are isolated points.

Make it easy for us to help you.

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Answer 1

Harald 2023-9-21

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2024082-how-to-detect-isolated-points-in-a-vector#answer_1315327

编辑：Harald 2023-9-21

在 MATLAB Online 中打开

outputVector.mat

Hi,

I believe this code does what you ask for:

load outputVector.mat

N = 500;

isolated = false(size(iidx));

L = length(iidx);

for k = 1:L

left = max(1,k-N):k-1;

right = k+1:min(L,k+N);

isolated(k) = ~any(iidx([left, right]) == iidx(k));

end

result = find(isolated);

plot(iidx, "*")

hold on

plot(result, iidx(isolated), "ro")

hold off

I don't see an obvious way to avoid the loop. If there are concerns about performance, I can think about it a bit more - or perhaps, others have an idea.

Note that it does not identify two of the points that you have circled. If you zoom in, you will see that there are two consecutive identical values there. My understanding is that you did not want to extract these, even though they look isolated on the first glance? If you wanted these, I do not fully understand the question yet.

Best wishes,

Harald