How to reshape 3D matrix ?

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

[DGM]

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]

I have edited the question with example.

Answer 1

[Stephen23]

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

[SojM]

How can it be done for large matrix of 36*42*7?

[Stephen23]

"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]

Thanks! It works

Answer 2

[Chunru]

% 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

[SojM]

How can it be done for large matrix of 36*42*7 to reshpae it into 7*2*756 in a simlar way?

[Chunru]

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]

Thanks. It worked.