How to exclude zeros in a matrix?

Question

Robert Flores 2019-4-3

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/454169-how-to-exclude-zeros-in-a-matrix

编辑： Jan 2019-4-4

Hello,

I am trying to get rid of the zero values in a matrix I have in V(:,:,i) in my for loop. However, I am getting an error, "Unable to perform assignment because the size of the left side is 297-by-448 and the size of the right side is 10611-by-1. Error in DIC_Data_Extraction (line 17) V(:,:,i) = nonzeros(data_dic_save.displacements(i).plot_v_ref_formatted);". Therfore, if you are able to help me out in resolving this error, it will be most appreciated, thanks. Below is a copy of my code. Also, unfortunatley, I can not attach my work space, so I hope this is enough information for you to help me out, thanks.

-Robert

% The displacements in the Y-direction 
V = zeros(297,448);
% Vyy = zeros{20863,1};
for i = 1:8 
    V(:,:,i) = nonzeros(data_dic_save.displacements(i).plot_v_ref_formatted);
%     Vyy{i} = {nonzeros(V(:,:,i))}
    avg(i) = abs(mean(mean(V(:,:,i))));
    med(i) = median(median(V(:,:,i)));
   
end

4 个评论
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Adam Danz 2019-4-3

From your description, it seems like zeros aren't the problem. Your nonzeros() function is producing a columnar vector with 10611 elements and you're trying to store that in a 297x448 matrix.

Robert Flores 2019-4-3

Adam Danz, that is exactly my issue. I am sorry for my late response, but that is the issue I am dealing with.

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Answer 1

Jan 2019-4-3

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/454169-how-to-exclude-zeros-in-a-matrix#answer_368907

编辑：Jan 2019-4-4

在 MATLAB Online 中打开

The cell is the right approach:

for i = 1:8 
    Vyy{i} = nonzeros(data_dic_save.displacements(i).plot_v_ref_formatted);
    avg(i) = abs(mean(Vyy{i}));
    med(i) = median(Vyy{i});
end

Other have explained already, that arrays must be rectangular.

Another option would be to set the zeros to NaN:

V = zeros(297, 448, 8);  % Pre-allocate all 3 dimensions!
for i = 1:8 
    aV          = data_dic_save.displacements(i).plot_v_ref_formatted;
    aV(aV == 0) = NaN;
    V(:, :, i)  = aV;
    
    avg(i) = abs(mean(aV, 'all', 'omitnan'));
    med(i) = median(aV, 'all', 'omitnan');  % See comments
end

Attention: I guessed, that you want the median of all values. Then median(X, 'all') is equivalent to median(X(:)), which is not necessarily the same as median(median(X, 1), 2). With nonzeros the output is a vector and there is no difference. Please check this explicitly.