# How can I repeat a 2-D array to create a 3-D array?

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Steve Francis on 12 Jul 2022
Commented: Voss on 13 Jul 2022
A is a 2x3 array. I want to create a 3-D 'stack' so that each layer of the 3-D stack is identical to A. I've found that the following code gives the desired result:
A =[1 2 3;4 5 6];
for j=1:5
B(j,:,:)=A;
end
disp (squeeze(B(3,:,:))) % an example showing that any layer of the 3-D array is the same as A
Is there a more elegant way to do this? I tried using repmat but couldn't get the same result.
Stephen23 on 13 Jul 2022
"That way the 2D slices are contiguous in memory..."
which also means that James Tursa's recommended approach will be more efficient (assuming that you mostly want to access those matrices).

Bruno Luong on 12 Jul 2022
A =[1 2 3;4 5 6];
B = repmat(reshape(A, [1 size(A)]),[5 1 1])
B =
B(:,:,1) = 1 4 1 4 1 4 1 4 1 4 B(:,:,2) = 2 5 2 5 2 5 2 5 2 5 B(:,:,3) = 3 6 3 6 3 6 3 6 3 6
##### 2 CommentsShowHide 1 older comment
Bruno Luong on 13 Jul 2022
Edited: Bruno Luong on 13 Jul 2022
EDIT : my deleted comment moves here
If you do repeat 3rd dimension few other approaches
A =[1 2 3;4 5 6]; N = 2;
B = repmat(A,[1,1,N]), % James's comment
B =
B(:,:,1) = 1 2 3 4 5 6 B(:,:,2) = 1 2 3 4 5 6
B = repelem(A,1,1,N),
B =
B(:,:,1) = 1 2 3 4 5 6 B(:,:,2) = 1 2 3 4 5 6
B = A(:,:,ones(1,N)),
B =
B(:,:,1) = 1 2 3 4 5 6 B(:,:,2) = 1 2 3 4 5 6
B = A + zeros(1,1,N),
B =
B(:,:,1) = 1 2 3 4 5 6 B(:,:,2) = 1 2 3 4 5 6

Voss on 12 Jul 2022
% what you have now:
A =[1 2 3;4 5 6];
for j=1:5
B(j,:,:)=A;
end
% another way, using repmat and permute:
B_new = repmat(permute(A,[3 1 2]),5,1);
% the result is the same:
isequal(B_new,B)
ans = logical
1
##### 2 CommentsShowHide 1 older comment
Voss on 13 Jul 2022
You're welcome!

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