Find indices where runs of zeros and ones ends

Question

Awais Saeed 2021-8-3

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/891662-find-indices-where-runs-of-zeros-and-ones-ends

编辑： Stephen23 2021-8-4

采纳的回答： Jonas

在 MATLAB Online 中打开

Assuming that I have a vector

H = [0 0 0 0 1 1 1 1 0 1 0 1 0 0 0 0 0];

I want to know the indices where long runs of 1's and 0's ends. Let's say if a bit repeats 4 times or greater, then it is a run of length greater than 4. According to this, I want to know the indices where all runs ends. First run is of zeros which ends at index 4. Second run is of ones which ends at 8. Third run is of zeros again and it ends at 17.

So far, I am able to count the run length only as following

i = find(diff(H));
run_length = [i numel(H)] - [0 i];
run_length =
     4     4     1     1     1     1     5

However, the needed answer is [4 8 17]. cumsum would not work because it will give cummulative sum of whole vector as

cumsum(run_length)
ans =
     4     8     9    10    11    12    17

Any suggestions will be helpful.

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Answer 1

Jonas 2021-8-3

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/891662-find-indices-where-runs-of-zeros-and-ones-ends#answer_759972

i would use

H = [0 0 0 0 1 1 1 1 0 1 0 1 0 0 0 0 0];
Hstr=erase(num2str(H),' ');
[~,onesEnds]=regexp(Hstr,{'0000+','1111+'});
sort(cell2mat(onesEnds))

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Awais Saeed 2021-8-4

Yes, this one is more flexible. Thank you.

Stephen23 2021-8-4

编辑：Stephen23 2021-8-4

在 MATLAB Online 中打开

Simpler and more efficient:

H = [0,0,0,0,1,1,1,1,0,1,0,1,0,0,0,0,0];
S = sprintf('%u',H);
X = regexp(S,'(0{4,}|1{4,})','end') % only zeros and ones
X = 1×3
     4     8    17
X = regexp(S,'(.)(??$1{3,})','end') % any character
X = 1×3
     4     8    17