I have 100 2D matrix .. After each matrix, I calculate the sum of elements inside it .. I want to see only the matrices with summation result under certain value (such as: 23). How can I do this?

I have 100 2D matrix .. After each matrix, I calculate the sum of elements inside it .. I want to see only the matrices with summation result under certain value (such as: 23). How can I do this?

[James Tursa]

How are the 2D matrices stored? As part of a 3D array? As distinct variable names? In a cell array? On the fly in a loop? Or ...?

[Mahmoud Ahmed]

stored in distinct variable name

[Stephen23]

@Mahmoud Ahmed: storing them as separate variables is not a good way to write code. It will make your code slow, buggy, complicated, and hard to debug:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

The best solution is to store your data in one 3D array. Then your task is trivially easy using indexing.

Answer 1

[Star Strider]

I have no idea how your matrices are stored or organised.

One approach:

M3 = randi(3, 5, 5, 10);                                    % Create Data
N = size(M3,3);
for k1 = 1:N
    MN = M3(:,:,k1);                                        % Define Matrix For This Loop Iteration
    Msum = sum(MN(:));                                      % Matrix Sum
    Mtx(k1) = k1 * (Msum < 23);                             % Save Index If ‘Msum < 23’, Else 0
end

Answer 2

[James Tursa]

E.g., if they were stored in a 3D array:

>> m = randi(10,3,3,5)  % some random data
m(:,:,1) =
     5     8     7
     5     8     7
     7     3     2
m(:,:,2) =
     2     4     8
     5     6     3
    10     3     6
m(:,:,3) =
     7     6     3
     9     2     9
    10     2     3
m(:,:,4) =
     9     4     7
     3     2     5
    10     3     4
m(:,:,5) =
     9    10     8
     6     3     4
     6     8     6
>> x = sum(reshape(m,[],size(m,3)))<50  % logical indexes where 2D sum is < 50
x =
     0     1     0     1     0
>> s = m(:,:,x)  % the 2D subsets that have the desired sum
s(:,:,1) =
     2     4     8
     5     6     3
    10     3     6
s(:,:,2) =
     9     4     7
     3     2     5
    10     3     4

Answer 3

[Stephen23]

Well, this is trivial if you store your data correctly in one array:

>> A = randi(8,2,2,100); % one hundred 2x2 matrices
>> idx = sum(sum(A,1),2)>23;
>> A(:,:,idx)
ans(:,:,1) =
     7     2
     8     8
ans(:,:,2) =
     8     2
     8     8
ans(:,:,3) =
     4     7
     8     8
ans(:,:,4) =
     8     7
     3     7
ans(:,:,5) =
     8     4
     8     4
ans(:,:,6) =
     5     7
     5     7
ans(:,:,7) =
     3     8
     8     5
ans(:,:,8) =
     1     8
     8     7
ans(:,:,9) =
     4     6
     7     8
ans(:,:,10) =
     8     5
     5     7
ans(:,:,11) =
     8     7
     6     4
ans(:,:,12) =
     7     6
     8     3