How to find out point of change of sequence of ones and zeros?

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Hello,
I have this matrice:
1 NaN 3.28000000000000
1 NaN 3.32000000000000
1 NaN 3.36000000000000
1 NaN 3.40000000000000
0 0.0320040000000000 3.44000000000000
0 0.0697230000000000 3.48000000000000
0 0.124815600000000 3.52000000000000
0 0.158877000000000 3.56000000000000
and I would like to have another column where would be just the number where the first column changes from 1 to 0.
Result should be like this:
1 NaN 3.28000000000000
1 NaN 3.32000000000000
1 NaN 3.36000000000000
1 NaN 3.40000000000000 3.40000000000000
0 0.0320040000000000 3.44000000000000
0 0.0697230000000000 3.48000000000000
0 0.124815600000000 3.52000000000000
0 0.158877000000000 3.56000000000000

Accepted Answer

Jan
Jan on 27 Jul 2021
Edited: Jan on 28 Jul 2021
What do you expect in the other rows of the 4th column? All rows must have the same number of columns, according to the definition of a matrix. If zeros are fine:
index = find(A(:, 1) == 0, 1) - 1; % [EDITED, -1 appended]
if any(index)
A(index, 4) = A(index, 3);
end
  5 Comments
Jan
Jan on 28 Jul 2021
Now you post another input, but do not mention, what you expect as output.
  • If you still want to use the first change from 1 to 0, use the code of my answer.
  • If you want to find all changes from 1 to 0:
index = strfind(A(:, 1).', [1, 0]);
B = A(index, 3);
% Alternative:
index = diff(A(:,1)) < 0;

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