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

2 views (last 30 days)
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.
  5 Comments
Stephen23
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).

Sign in to comment.

Accepted Answer

Bruno Luong
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 Comments
Bruno Luong
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

Sign in to comment.

More Answers (1)

Voss
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

Tags

Products


Release

R2020b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!