count of non zero elements of a row vector in a loop

Question

Georgios Kirkinezos 2020-10-28

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/628653-count-of-non-zero-elements-of-a-row-vector-in-a-loop

评论： Peter O 2020-10-28

采纳的回答： Peter O

在 MATLAB Online 中打开

Hi everyone,

i want to count the nonzero elements of a row-vector in a loop, i have the initial (360,1000) matrix u_new

for i=1:360;
    for j=1:1000;
        if u_new(i,j)==0               %%% here i transformed zeros to Nan, to use the following command isnan 
            u_new(i,j)=NaN;
            insample_u_new=isnan(u_new(i,:))==0;     %%% in this row-vector the possible values are 0 or 1, i am interested in getting the number of ones
            P = numel(insample_u_new(i,j)~= 0);   %%%here is the problem
        end
    end
end

I want the output P to be the number of the nonzero elements (ones) from the row-vector u_new=u(:,1:1000) for the loop.

Thanks for your answers in advance.

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Answer 1

Peter O 2020-10-28

1
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https://ww2.mathworks.cn/matlabcentral/answers/628653-count-of-non-zero-elements-of-a-row-vector-in-a-loop#answer_526458

在 MATLAB Online 中打开

Try the nnz function.

It sounds like you're trying to count the number of nonzero elements in each row? Use arrayfun to apply this function to each row of the matrix (extracting the row index).

NZ = arrayfun(@(ix) nnz(u_new(ix,:)),1:size(u_new,1))

NZ will be a 1 x n_rows vector containing the nonzero element counts for each row.