Detect parts of a 0/1 (binary) vector consisting of only 0 or 1

Question

Ilya 2014-4-3

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/124355-detect-parts-of-a-0-1-binary-vector-consisting-of-only-0-or-1

编辑： Ilya 2014-4-6

采纳的回答： Sean de Wolski

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Let's say I have a vector of 0 and 1:

a=[1 1 1 0 0 0 1 0 1 0 0 1 1 0];

It's needed to find a way to extract the vector's indices so that each group of extracted indices contains a part of a vector consisting of only zeros or only ones. For the given example it should be like:

[1 3] [4 6] [7] [8] [9] [10 11] [12 13] [14]

I thought about diff(), but some post-processing is definitely required after it...

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Answer 1

Sean de Wolski 2014-4-3

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https://ww2.mathworks.cn/matlabcentral/answers/124355-detect-parts-of-a-0-1-binary-vector-consisting-of-only-0-or-1#answer_131963

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idx = find(diff([~a(1) a]))';
pcs = spdiags(rot90([idx-1 idx]));
pcs(end) = numel(a)

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Image Analyst 2014-4-3

Wow - never would have guessed that.

Ilya 2014-4-6

编辑：Ilya 2014-4-6

在 MATLAB Online 中打开

A more robust solution (the same idea):

idx1 = find(diff([~a(1) a]));
idx2 = circshift(idx1-1,[0 -1]);
idx2(end) = numel(a);
pcs = [idx1; idx2];

The initial one may be wrong i.e. in case a=[1 1 1 1 0], due to the unpredictable spdiags() behavior.

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Answer 2

Image Analyst 2014-4-3

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https://ww2.mathworks.cn/matlabcentral/answers/124355-detect-parts-of-a-0-1-binary-vector-consisting-of-only-0-or-1#answer_131962

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If you have the Image Processing Toolbox, the 1's are given by the PixelIdxList property. You can do it in one line with a call to regionprops:

a=[1 1 1 0 0 0 1 0 1 0 0 1 1 0];
% Find 1's.
locations = regionprops(logical(a), 'PixelIdxList');
% Print out to command line:
for k = 1 : length(locations)
  locations(k).PixelIdxList
end
% Find 0's.
locations = regionprops(logical(~a), 'PixelIdxList');
% Print out to command line:
for k = 1 : length(locations)
  locations(k).PixelIdxList
end