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

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Steve Francis
Steve Francis 2022-7-12
评论： Voss 2022-7-13
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.
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Steve Francis
Steve Francis 2022-7-13
Thanks again, James. You're right. Damn, I wish I'd thought about this earlier. I will spend some time seeing if I can re-write my scripts
Stephen23
Stephen23 2022-7-13
"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).

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采纳的回答

Bruno Luong
Bruno Luong 2022-7-12
Ran in:
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 个评论
Bruno Luong
Bruno Luong 2022-7-13
编辑：Bruno Luong 2022-7-13
Ran in:
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

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更多回答（1 个）

Voss
Voss 2022-7-12
Ran in:
% 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

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