MATLAB: Reshaping/vectorizing a n-d matrix to a vector along each dimension

reshapevectors

Lets say I have a matrix given by

    a=randn(4,4,5);

How do I get a 80*1 vector along each dimension. That is the new vector vec B should look like the following

    B=[a(1,1,1),a(1,1,2),..a(1,1,5),a(1,2,1),..,a(1,2,5),...a(4,4,5)]'

Both the below commands will not give this

    B=a(:);
    B=reshape(a,[80,1]);

Best Answer

result = reshape(permute(a,[3 2 1]),[],1);

Related Solutions

MATLAB: N-D matrix accumarray

Yes, accumarray will do it easily. You just need to generate the correct subscripts for it, which is the cartesian product of all the indices in all the dimension, replacing the appropriate dimensions with your grouping variables:

A = randi(100, [3 4 2 7]);  %demo data
%generate indices in all the dimension, and replace appropriate one with grouping variables:
indices = arrayfun(@(s) 1:s, size(A), 'UniformOutput', false); %vector of indices in each dimension
indices{2} = [2 1 2 3];  %grouping in 2nd dimension
indices{4} = [3 3 2 1 3 2 4];  %grouping in 4th dimension
%calculate cartesian product of indices
[indices{:}] = ndgrid(indices{:});
indices = cell2mat(cellfun(@(v) v(:), indices, 'UniformOutput', false));
%apply accumarray with default sum function
B = accumarray(indices, A(:));

Edit: note that the above will work with arrays of any dimension (within reason, ndgrid will run out of memory for too many dimensions).

MATLAB: Rotating N-D matrices

Use a for-loop over the pages and imrotate

Something like:

X = your_original_2d_image
Xrot = zeros([size(X) 24],'like',X);
for ii = 1:24
   Xrot(:,:,ii) = imrotate(X,7.5*ii,'crop')
end

Best Answer

Related Solutions

MATLAB: N-D matrix accumarray

MATLAB: Rotating N-D matrices

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