Matrix Data Results Explanation

Question

Augusto Gabriel da Costa Pereira 2023-9-16

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https://ww2.mathworks.cn/matlabcentral/answers/2022002-matrix-data-results-explanation

评论： Dyuman Joshi 2023-9-16

I used the following code, and you can see that in the second row of the fourth column, the result is zero and not NaN; it should be NaN as the result.

%
soma_total = nan(3, 4);
data1 = [nan nan 1 2; 1 2 nan nan; 1 2 nan nan];
data2 = [5 5 nan nan; 2 1 1 nan; nan nan 1 1];
% 
result = nansum(cat(3, soma_total, data1, data2), 3);
% 
disp(result);

The result was:

[5 5 1 2;

3 3 1 0;

1 2 1 1]

The result should be:

[5 5 1 2;

3 3 1 NaN;

1 2 1 1]

Does anyone have an idea to solve this?

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Answer 1

Dyuman Joshi 2023-9-16

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https://ww2.mathworks.cn/matlabcentral/answers/2022002-matrix-data-results-explanation#answer_1311862

编辑：Dyuman Joshi 2023-9-16

在 MATLAB Online 中打开

nansum does not do what you are expecting it to do. Also, using nansum() is not recommended as you can see from its documentation page. Use sum instead -

Here's a workaround -

%
soma_total = nan(3, 4);
data1 = [nan nan 1 2; 1 2 nan nan; 1 2 nan nan];
data2 = [5 5 nan nan; 2 1 1 nan; nan nan 1 1];
%Dimension to operate on
dim = 3;
%defining the array
arr = cat(dim, soma_total, data1, data2);
%Finding indices for all elements which are NaN corresponding to the "dim" dimension
idx = all(isnan(arr),dim)
idx = 3×4 logical array
   0   0   0   0
   0   0   0   1
   0   0   0   0
%If you want to use nansum instead, use this command
%result = nansum(arr,dim)
result = sum(arr,dim,'omitnan')
result = 3×4
     5     5     1     2
     3     3     1     0
     1     2     1     1
%Converting the respective values back to NaN
result(idx) = NaN
result = 3×4
     5     5     1     2
     3     3     1   NaN
     1     2     1     1