find sum of the run length of non zero elements between zeros of a matrix

suppose my matrix is

a=[ 1 2 3 0 0 0 4 5 6 0 0 0 7 8 0 0 9 0 0 ]

output wanted is

[6 15 15 9]

Answer 1

[Walter Roberson]

a = [ 1 2 3 0 0 0 4 5 6 0 0 0 7 8 0 0 9 0 0 ]

a = 1×19

1 2 3 0 0 0 4 5 6 0 0 0 7 8 0 0 9 0 0

mask = logical(a);
starts = strfind([0 mask], [0 1]);
stops = strfind([mask 0], [1 0]) + 1;
ca = cumsum([0 a]);
ca(stops) - ca(starts)

ans = 1×4

6 15 15 9

Answer 2

[Soniya Jain]

a=[ 1 2 3 0 0 0 4 5 6 0 0 0 7 8 0 0 9 0 0 ];
j = 0;
i = 1;
while i ~= (length(a)+1)
    if a(i)~=0
        sum = 0;
        while a(i)~=0
            sum = sum + a(i);
            i = i + 1;
        end
        j = j + 1;
        res(j) = sum;
    end
    i = i + 1;
end

Here is the code of it, but if you are not familiar with how to write MATLAB code, then you can start with the MATLAB Onramp tutorial to quickly learn the essentials of MATLAB.

[PRIYAM DEKA]

this code works but if the last element is non zero the code doesnot work.

though it can be corrected by defining a=[a 0] before the while loop.

thank you

[Soniya Jain]

Oh yes, thanks for noticing that!

Answer 3

[Simon Chan]

a=[ 1 2 3 0 0 0 4 5 6 0 0 0 7 8 0 0 9 0 0 ];
pos=diff(a)<0;                                  % Position before hitting a zero
c=cumsum(a);                                    % Cumulative sum
d=[0 c(pos)];                                   % Add a zero in the first position, otherwise first value will be lost
diff(d)

[PRIYAM DEKA]

this code doesnot work if i have a higher no before a lower

Answer 4

[Matt J]

Using this File Exchange submission

https://www.mathworks.com/matlabcentral/fileexchange/78008-tools-for-processing-consecutive-repetitions-in-vectors

it is quite easy.

result=groupFcn(@sum, a, groupTrue(a~=0))

Answer 5

[Image Analyst]

Here's another way:

a = [ 1 2 3 0 0 0 4 5 6 0 0 0 7 8 0 0 9 0 0 ]
% Extract each run:
props = regionprops(logical(a), a, 'PixelValues')
% Sum up each run.
for k = 1 : length(props)
	theSums(k) = sum(props(k).PixelValues)
end