Reshape a 'column' matrix into a 'row' matrix

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Moreno, M. 2022-4-10

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https://ww2.mathworks.cn/matlabcentral/answers/1693315-reshape-a-column-matrix-into-a-row-matrix

评论： Moreno, M. 2022-4-11

Hi, I hope you are well.

I have a matrix 'X' that is generated through a series of parameters, that in the end of the day is a column-wise concatenated matrix such as:

X = [A; B; C; ...; P], where A, B, C, ..., P are 'p' equally-sized [m - 1, q] matrices.

My goal is to reshape this matrix in a way that the new matrix 'X' is:

X = [A, B, C, ..., P]

Ideally, this would be done without loops or manually, so that the operation could be vectorised. A representative example to solve 'similar' to my case matrix would be:

m = 8;
p = 2;
q = 10;
X = rand(p * (m - 1), q);
X(:, [1, q]) = 0;

Which would be a random matrix made of 2 (p) submatrices of [7, 10] ([m - 1, q]) elements. The final solution that I am seeking would be, for this particular case:

Y = [X(1 : m - 1, :), X(m : 2 * (m - 1), :)];

Some help on how to do this transformation for a generic number of matrices 'p' of dimension [m - 1, q] via the reshape command, circshift, rot90, transpose or similar would be greatly appreciated, so that the transformation was compact.

Thanks in advance and regards,

Moreno, M.

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Answer 1

DGM 2022-4-10

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https://ww2.mathworks.cn/matlabcentral/answers/1693315-reshape-a-column-matrix-into-a-row-matrix#answer_939670

在 MATLAB Online 中打开

There are other ways this could be done, but just using reshape() and permute() is often the fastest:

m = 5;
p = 2;
q = 5;
X = rand(p * (m - 1), q);
X(:, [1, q]) = 0
X = 8×5
         0    0.4353    0.6008    0.1466         0
         0    0.9317    0.9804    0.1811         0
         0    0.9719    0.7923    0.6327         0
         0    0.3685    0.4549    0.4899         0
         0    0.9231    0.8038    0.1596         0
         0    0.3666    0.9581    0.8240         0
         0    0.8689    0.9033    0.3245         0
         0    0.3822    0.8846    0.7878         0
% given example
Y = [X(1 : m - 1, :), X(m : 2 * (m - 1), :)]
Y = 4×10
         0    0.4353    0.6008    0.1466         0         0    0.9231    0.8038    0.1596         0
         0    0.9317    0.9804    0.1811         0         0    0.3666    0.9581    0.8240         0
         0    0.9719    0.7923    0.6327         0         0    0.8689    0.9033    0.3245         0
         0    0.3685    0.4549    0.4899         0         0    0.3822    0.8846    0.7878         0
% using reshape()
Y = reshape(permute(reshape(X.',q,m-1,p),[1 3 2]),[],m-1).'
Y = 4×10
         0    0.4353    0.6008    0.1466         0         0    0.9231    0.8038    0.1596         0
         0    0.9317    0.9804    0.1811         0         0    0.3666    0.9581    0.8240         0
         0    0.9719    0.7923    0.6327         0         0    0.8689    0.9033    0.3245         0
         0    0.3685    0.4549    0.4899         0         0    0.3822    0.8846    0.7878         0