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

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Steve Francis il 12 Lug 2022
Commentato: Voss il 13 Lug 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.
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Steve Francis il 13 Lug 2022
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 il 13 Lug 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).

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Bruno Luong il 12 Lug 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
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Steve Francis il 13 Lug 2022
Modificato: Steve Francis il 13 Lug 2022
Thanks very much!
Bruno Luong il 13 Lug 2022
Modificato: Bruno Luong il 13 Lug 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

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Più risposte (1)

Voss il 12 Lug 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
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Steve Francis il 13 Lug 2022
Thank you, Voss.
Voss il 13 Lug 2022
You're welcome!

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