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

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Woonsup Choi
Woonsup Choi 2015-11-24
评论： Star Strider 2015-11-24
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!

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Star Strider
Star Strider 2015-11-24
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.
  2 个评论
Woonsup Choi
Woonsup Choi 2015-11-24
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
Star Strider 2015-11-24
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.

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