How to count the number of consecutive identical elements (in both the directions) in a binary vector ?
104 views (last 30 days)
Show older comments
Suppose I have a binary vector
X = [0 0 0 0 1 1 1 0 1 1 1 1]
I want to characterize each element with the number of identical elements occurring in consecutive positions in both the directions. For instance, the desired output should look like:
Y = [4 4 4 4 3 3 3 1 4 4 4 4].
I found a similar thread, but it counts only in the forward direction. Thanks in advance for any sort of assistance.
1 Comment
Guillaume
on 11 Feb 2018
I'm not sure I understand the concept of direction for identical consecutive elements. Identity is not directional.
Accepted Answer
Jan
on 11 Feb 2018
Edited: Jan
on 11 Feb 2018
X = [0 0 0 0 1 1 1 0 1 1 1 1];
[B, N] = RunLength(X);
Y = RunLength(N, N);
If you do not have a C-compiler for the fast C-Mex function, use RunLength_M.
Or with Matlab code:
d = [true, diff(X) ~= 0, true]; % TRUE if values change
n = diff(find(d)); % Number of repetitions
Y = repelem(n, n)
2 Comments
More Answers (2)
Jos (10584)
on 11 Feb 2018
Edited: Jos (10584)
on 11 Feb 2018
Something like this?
X = [0 0 0 0 1 1 1 0 1 1 1 1] % row vector!
numX = numel(X) ;
Q = find([false diff(X)≈0]) ;
I = zeros(1, numX) ;
I(Q) = 1 ;
I = cumsum(I) ;
N = diff([1 Q numX+1]) ;
result = N(I+1)
0 Comments
Image Analyst
on 11 Feb 2018
Here's yet another way:
X = logical([0 0 0 0 1 1 1 0 1 1 1 1])
Y = zeros(1, length(X)); % Initialize output as the same size as X.
props = regionprops(X, 'Area', 'PixelIdxList');
for k = 1 : length(props)
Y(props(k).PixelIdxList) = props(k).Area;
end
props = regionprops(~X, 'Area', 'PixelIdxList');
for k = 1 : length(props)
Y(props(k).PixelIdxList) = props(k).Area;
end
0 Comments
See Also
Categories
Find more on Startup and Shutdown in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!