How to reshape 3D matrix ?

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SojM
SojM 2021-7-22
评论： SojM 2021-7-22
I have a 3D matrix of 36*42*7 dimension. I want to reshape it in such a way that I extract two colums from each third dimension. That means my final matrix dimension would be 7*2*756. How can I do this?
For example, Assume I have 4*4*3 matrix
A1= [a b c d; e f g h; i j k l; m n o p]
A2= [q r s t; u v w x; y z A B; C D E F]
A3= [G H I J; K L M N; O P Q R; S T U V ]
Now I want to reshape it to 3*2*8 such that
B1= [a b; q r; G H]
B2=[c d; s t; I J]
B3=[e f; u v; K L]
B4..... B8
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DGM
DGM 2021-7-22
Ran in:
Your question is ambiguous. There are a number of ways 10584 elements can be reshaped from one array to another with the same number of elements. If one assumes that everything should be columnwise, then you can just use reshape()
A = rand(36,42,7);
B = reshape(A,7,2,756);
size(B)
ans = 1×3
7 2 756
Otherwise, you'll have to explain how you want the data to be oriented.
SojM
SojM 2021-7-22
I have edited the question with example.

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采纳的回答

Stephen23
Stephen23 2021-7-22
Ran in:
A = randi(9,4,4,3)
A =
A(:,:,1) = 5 7 6 6 7 8 8 1 7 3 8 7 5 1 5 4 A(:,:,2) = 5 6 2 4 2 9 6 2 3 3 2 2 5 1 5 6 A(:,:,3) = 6 9 8 5 1 7 7 9 5 8 5 3 6 5 5 9
B = permute(reshape(permute(A,[2,1,3]),[2,8,3]),[3,1,2])
B =
B(:,:,1) = 5 7 5 6 6 9 B(:,:,2) = 6 6 2 4 8 5 B(:,:,3) = 7 8 2 9 1 7 B(:,:,4) = 8 1 6 2 7 9 B(:,:,5) = 7 3 3 3 5 8 B(:,:,6) = 8 7 2 2 5 3 B(:,:,7) = 5 1 5 1 6 5 B(:,:,8) = 5 4 5 6 5 9
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Stephen23
Stephen23 2021-7-22
"How can it be done for large matrix of 36*42*7 to reshpae it into 7*2*756 in a simlar way?"
B = permute(reshape(permute(A,[2,1,3]),[2,756,7]),[3,1,2])
% ^ ^^^ ^
SojM
SojM 2021-7-22
Thanks! It works

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更多回答（1 个）

Chunru
Chunru 2021-7-22
Ran in:
% Generate data (using number 1,...48 to represent a,...V)
Z = permute(reshape(1:48, [4 4 3]), [2 1 3])
Z =
Z(:,:,1) = 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Z(:,:,2) = 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Z(:,:,3) = 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
% First permute the dimension so that a,b,c,.. are along the 1st dim
Z1 = permute(Z, [2 1 3])
Z1 =
Z1(:,:,1) = 1 5 9 13 2 6 10 14 3 7 11 15 4 8 12 16 Z1(:,:,2) = 17 21 25 29 18 22 26 30 19 23 27 31 20 24 28 32 Z1(:,:,3) = 33 37 41 45 34 38 42 46 35 39 43 47 36 40 44 48
% No reshape
Z2 = reshape(Z1, [2 8 3])
Z2 =
Z2(:,:,1) = 1 3 5 7 9 11 13 15 2 4 6 8 10 12 14 16 Z2(:,:,2) = 17 19 21 23 25 27 29 31 18 20 22 24 26 28 30 32 Z2(:,:,3) = 33 35 37 39 41 43 45 47 34 36 38 40 42 44 46 48
% permute
Z3 = permute(Z2, [3 1 2])
Z3 =
Z3(:,:,1) = 1 2 17 18 33 34 Z3(:,:,2) = 3 4 19 20 35 36 Z3(:,:,3) = 5 6 21 22 37 38 Z3(:,:,4) = 7 8 23 24 39 40 Z3(:,:,5) = 9 10 25 26 41 42 Z3(:,:,6) = 11 12 27 28 43 44 Z3(:,:,7) = 13 14 29 30 45 46 Z3(:,:,8) = 15 16 31 32 47 48
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Chunru
Chunru 2021-7-22
Exactly same:
Z = rand(36, 42, 7);
Z1 = permute(Z, [2 1 3]);
Z2 = reshape(Z1, [2 756 7]); %2x756 = 36*42
Z3 = permute(Z2, [3 1 2]);
Or you can combine the three statements in on as in @Stephen Cobeldick's answer.
SojM
SojM 2021-7-22
Thanks. It worked.

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