# How to correctly store and access data in a 4D array?

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Luqman Saleem on 4 Mar 2024
Edited: Stephen23 on 4 Mar 2024
Suppose I store some 2-by-2 matrices in a 4D array as following
data = zeros(10,5,2,2);
for i = 1:10
for j = 1:5
a = [i+j, 0;
i-j, 0];
data(i,j,:,:) = a;
end
end
later, I want to acess these 2-by-2 matrices. How can I correctly access them? Is the following way a correct way?
i = 2;
j = 5;
matrix = reshape( data(i,j,:,:), 2, 2)
I have tested this method for several i and j. it seems to work, but I am not sure if this always gives correct result.
##### 2 CommentsShow NoneHide None
Dyuman Joshi on 4 Mar 2024
"Is the following way a correct way?"
Yes, it is correct.
Stephen23 on 4 Mar 2024
Edited: Stephen23 on 4 Mar 2024
"Is the following way a correct way?"
It seems to be. If you permute the dimensions of that matrix then you would not need to RESHAPE all the time.
Note: explicit RESHAPE is better than uncontrolled SQUEEZE.

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### Answers (1)

Hassaan on 4 Mar 2024
Edited: Hassaan on 4 Mar 2024
It can be and other way could be:
% Initialize a 4D array to store 2-by-2 matrices
data = zeros(10,5,2,2);
% Fill the array with 2-by-2 matrices
for i = 1:10
for j = 1:5
a = [i+j, 0;
i-j, 0];
data(i,j,:,:) = a;
end
end
% Access a specific 2-by-2 matrix without reshape
i = 2;
j = 5;
matrix = squeeze(data(i,j,:,:));
% Display the accessed matrix
disp(matrix);
7 0 -3 0
-----------------------------------------------------------------------------------------------------------------------------------------------------
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It's important to note that the advice and code are based on limited information and meant for educational purposes. Users should verify and adapt the code to their specific needs, ensuring compatibility and adherence to ethical standards.
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