How to construct a 3x9 matrix E from a 3x3x3 matrix D, where D(x,y,:) is the column of E?

A = [1 2 3; 4 5 6; 7 8 9];
B = [11 22 33; 44 55 66; 77 88 99];
C = [111 222 333; 444 555 666; 777 888 999];
D = cat(3,A,B,C);

How to construct a 3x9 matrix E, where E(:,1) = D(1,1,:), E(:,2)=D(1,2,:), E(:,3)=D(1,3,:), ..., E(:,9)=D(3,3,:)?

What if D is a 3 x m x n matrix? How to construct a 2D (3x mn) matrix E from D, where D(x,y,:) becomes the column of E? Thank you.

Answer 1

[Image Analyst]

A = [1 2 3; 4 5 6; 7 8 9];
B = [11 22 33; 44 55 66; 77 88 99];
C = [111 222 333; 444 555 666; 777 888 999];
D = cat(3,A,B,C)
E = [reshape(D(:, :, 1), [], 1), reshape(D(:, :, 2), [], 1), reshape(D(:, :, 3), [], 1)]

E =

1 11 111

4 44 444

7 77 777

2 22 222

5 55 555

8 88 888

3 33 333

6 66 666

9 99 999