How can I count the number of elements in a row satisfying a condition?

I have a vector looking like [0; 0; 0; -1.2; -0.4; 0; 0; 0; -3; -1.2; -2]. The non-zero numbers appear in two sequences. First, two of them in a row, and second, three of them. I would like to obtain an answer like [2;3], counting the number of elements in each sequence of non-zero values.

Thank you!

Answer 1

[Star Strider]

One approach:

A = [0; 0; 0; -1.2; -0.4; 0; 0; 0; -3; -1.2; -2];
dA = [find(diff([A ~= 0])); length(A)];                 % Detect Start, End Indices
dAr = reshape(dA, 2, []);                               % Reshape Into 2xN Matrix
Result = diff(dAr)                                      % Subtract Columns

Result =
     2     3

I don’t know how robust this is, but it works here.

[Woonsup Choi]

Thank you for the quick answer. When dA has an odd number of elements, reshape did not work. I'll think about it.

[Star Strider]

My pleasure.

If ‘dA’ has an odd number of elements, you may need to eliminate the last one, ‘length(A)’. It is easy to test for that:

if rem(length(dA),2) ~= 0
    dA = dA(1:end-1);
end

before the reshape call.