how to scan a matrix row by row and save index of elements

Question

ali eskandari 2021-9-2

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1445559-how-to-scan-a-matrix-row-by-row-and-save-index-of-elements

编辑： Matt J 2021-9-2

A =
    2    3    4
5    5    6    2
    3    1    3  

I have a matrix-like A, and my aim is to scan the matrix row by row and save the index of values that is greater than 2 (or any threshold). In fact, I want to have an array like this:

H = {[3,4];[2,3];[1,2,4]}

I tried to do it like below but I don't know how I can append an elemnt to the end of array H.

If you can suggest anything faster way, I would appreciate it.

for i = 1:width(A)
    H{i} = [];
    for j = 1:height(A)
        if A(i,j) > 2
           H{i} =  % how to indicate the index of the matxis that is true for the if condition
        end
    end
end

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Matt J 2021-9-2

编辑：Matt J 2021-9-2

在 MATLAB Online 中打开

I wonder why you wouldn't simply use a sparse binarymatrix:

H=sparse(A>2);

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Answer 1

Matt J 2021-9-2

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1445559-how-to-scan-a-matrix-row-by-row-and-save-index-of-elements#answer_779659

编辑：Matt J 2021-9-2

在 MATLAB Online 中打开

A = [1      2    3    4
    0.5    5    6    2
    5      3    1    3] ;
[I,J]=find(A>2);
H=accumarray(I,J,[],@(x){x.'});
H{:}
ans = 1×2
     3     4
ans = 1×2
     2     3
ans = 1×3
     1     2     4