How to sum up a few numbers in sequence and save as a separate matrix

I have a matrix like [0; 0; -1; -2; -1; 0; 0; 0; -2; -1; 0]. From here I would like to sum up sequences of non-zero values and save the result in a separate matrix. From the example, the result should be [-4; -3]. How should I write the code?

Thank you.

Answer 1

[Jos (10584)]

Here is an algorithm:

A = [0; 0; -1; -2; -1; 0; 0; 0; -2; -1; 0] % input
B = cumsum(A)
tf = diff([A==0 ; true])==1
C = B(tf)
D = [C(1) ; diff(C)] % output

Answer 2

[Image Analyst]

An alternate way using the Image Processing Toolbox:

A = [0; 0; -1; -2; -1; 0; 0; 0; -2; -1; 0] % input
measurements = regionprops(logical(A~=0), A, 'Area', 'MeanIntensity');
allAreas = [measurements.Area]
allIntensities = [measurements.MeanIntensity]
integratedValues = allAreas .* allIntensities

Of course you could combine it all into 2 lines if you wanted it more compact (but more cryptic):

measurements = regionprops(logical(A~=0), A, 'Area', 'MeanIntensity');
integratedValues = [measurements.Area] .* [measurements.MeanIntensity]