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

Question

PRIYAM DEKA 2021-7-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/875933-find-sum-of-the-run-length-of-non-zero-elements-between-zeros-of-a-matrix

回答： Image Analyst 2021-7-11

采纳的回答： Walter Roberson

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]

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Answer 1

Walter Roberson 2021-7-10

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https://ww2.mathworks.cn/matlabcentral/answers/875933-find-sum-of-the-run-length-of-non-zero-elements-between-zeros-of-a-matrix#answer_744058

在 MATLAB Online 中打开

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

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Answer 2

Soniya Jain 2021-7-10

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https://ww2.mathworks.cn/matlabcentral/answers/875933-find-sum-of-the-run-length-of-non-zero-elements-between-zeros-of-a-matrix#answer_744023

在 MATLAB Online 中打开

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.

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PRIYAM DEKA 2021-7-10

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 2021-7-11

Oh yes, thanks for noticing that!

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Answer 3

Simon Chan 2021-7-10

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https://ww2.mathworks.cn/matlabcentral/answers/875933-find-sum-of-the-run-length-of-non-zero-elements-between-zeros-of-a-matrix#answer_744033

在 MATLAB Online 中打开

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)

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PRIYAM DEKA 2021-7-10

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

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Answer 4

Matt J 2021-7-10

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https://ww2.mathworks.cn/matlabcentral/answers/875933-find-sum-of-the-run-length-of-non-zero-elements-between-zeros-of-a-matrix#answer_744053

编辑：Matt J 2021-7-10

在 MATLAB Online 中打开

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))

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Answer 5

Image Analyst 2021-7-11

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https://ww2.mathworks.cn/matlabcentral/answers/875933-find-sum-of-the-run-length-of-non-zero-elements-between-zeros-of-a-matrix#answer_744438

在 MATLAB Online 中打开

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