Change matrix dimensions from 4D to 2 D : matrix manipulation

Dear Matlab community, I am still trying to manipulate some of my output here by converting 4D matrices to 2D. I am having a hard time using "squeeze" and "reshape". I have this matrix (5by5 by 14680 by 30)[ this is basically 30 sets of 14680 of 5by5 matrices), and I need to extract only all the 1st columns from each 5by5 matrices, to have 14680 of (5*1) arrays/matrices, then transpose the (5*1)' so my final matrix has the following dimensions : Final (14680by5) two dimensions only with each row(:,1:5) has the elements from the extracted (5*1) arrays from the step before. I would really appreciate any help! thank you matlab community! Amine

[Kenny Kim]

"I need to extract only all the 1st columns from each 5by5 matrices, to have 14680 of (5*1) arrays/matrices"

If you extract only the first column from each 5x5, then you get 5x1x14680x30. You need to tell us what you want to do with that last dimension.

[Matt J]

It would also be good to mention in what way this post is not redundant with respect to

http://www.mathworks.com/matlabcentral/answers/316590-matrix-manipulation-from-4d-to-2d

[Amine Ben Ayara]

Kenny & Matt, Sorry guys, I did make a mistake. So starting with a 4D matrix(5*5*14680*30), I need to first extract only the first column from every 5*5 matrix from within the bigger one. Then basically transpose that column to become (1*5) and stack all of the 14680 of them horizontally, then vertically across the last dimension so the final matrix size is on 2D as (14680 by 150) , where the number of columns 150=5*30 I hope I was more clear this time and sorry for the confusion. Kind Regards, Amine

Answer 1

[Walter Roberson]

   Output = squeeze( mat2cell( permute(YourMatrix,[3 1 2 4]), size(YourMatrix,3), size(YourMatrix,1), ones(1,size(YourMatrix,2)), ones(1,size(YourMatrix,4)) ) );

Output will now be a 5 x 30 cell array in which each element is a 14680 x 5 array formed by extracting first columns and making them rows.

[Amine Ben Ayara]

Hello Mr. Roberson, Thank you so much for the feedback. I ran your code and I got an output in form of 5by30 cell. I am not really familiar with the way it is produced as I only understand simpler dimensions and commands. Would you be kind enough to look at the screen-shot that I just took of the output and tell me if I did something wrong, or perhaps if I did not explain myself clearly. So suppose that my starting matrix is MS(5*5*14680*30) ( that is 14680 of 5 by 5 matrices and 30 sets of them, from my understanding). Now I need to extract only the first column from each (5by5) matrix from within the bigger matrix MS. Once that is done, I need to convert that column to a row (by transpose I think) so it becomes (1by5) and that is 14680 from within each set, so the final matrix output is then:(14680 by 150) ( two dimensions) I am assuming there is a way to stack all the 30 sets horizontally, hence (5 columns times 30= 150 columns ) Sorry, I must have not explained correctly earlier,

[Walter Roberson]

Output = reshape( permute( YourMatrix(:,1,:,), [3 1 4 2]), size(YourMatrix,3), []);

Answer 2

[Kenny Kim]

This should make the matrix you were looking for:

datatemp = permute(squeeze(data(:,1,:,:)),[2 1 3]);
datatemp = reshape(datatemp,[size(datatemp,1),size(datatemp,2)*size(datatemp,3)]);

where data is the variable name for your 4D matrix.