How can I rotate a part of a matrix

Hi there,

I have a 4D images (dimensions [156 192 26 42]). I would like to rotate only the last 20 volumes of my 4D matrix and keep the first as it is.

I tried the following:

rotated_matrix=original_matrix;
rotated_matrix = rot90(original_matrix(:,:,:,23:42));

The rotated_matrix has been rotated but it has dimensions [192 156 26 20]. Basically it contains the volumes that have been rotated.

How can I rotate only the volume in the last 20 places and keep the first 22 as they are?

Answer 1

[Ameer Hamza]

Try something like this

rotated_matrix = original_matrix(:,:,:,[1:20 42:-1:21]);

[DM]

Doesn't seem to be working..

[Ameer Hamza]

Ok. You wanted to rotate the last 20 only. There will be a minor modification. Does the following work?

rotated_matrix = original_matrix(:,:,:,[1:22 42:-1:23]);

[DM]

Yes only the first 20. The above line of code does it only concanate the rotated_matrix and the original_matrix?

It doesn't perform any rotation right?

[Ameer Hamza]

It reverse the order of last 20 elements in the 4th dimension. The other elements remain unchanged.

[DM]

I might have put my question wrong. I didn't want to reverse the order of the last 20 elements.

I wanted to replace the last 20 elements in the 4th dimension of the original matrix with the 20 elements of the rotated_matrix.

Origina matrix has dimensions [156 192 26 42] where the rotated matrix has dimensions [156 192 26 20].

What I wanted to do is to replace the last 20 elemets of the original matrix with the 20 elemets of the rotated matrix.

[Ameer Hamza]

Ok. I get it know. Following will work for this case

original_matrix(:,:,:,end-19:end) = rotated_matrix