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

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

Answer 1

[Jan]

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

[Lukas Poviser]

Zeros or maybe it would be better if the value were in new matrice

[Jan]

It is your decision.

index = find(A(:, 1) == 0, 1) - 1;
B     = A(index, 3);

[Lukas Poviser]

What if the sequence was longer and repeated? e.g.

A = [

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

1 NaN 4.3232

1 NaN 2.90

0 8.323 6.76

0 8.123 6.79

0 0.097230000000000 3.8000000000000

1 NaN 3.0600000000000

1 NaN 5.40000000000000

];

[Jan]

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;

[Lukas Poviser]

It works perfectly! Thanks!