MATLAB: Collapse across dimensions of a matrix

MATLABmatrix operationsmeanmulti-dimensionsal

I have a multidimensional matrix 19 x 64 x 5 x 21 which corresponds to 19 participants x 64 channels x 5 timepoints x 21 data values.

I want to collapse the last two dimensions of the matrix so that I end up with the mean of the (5 x 21) data values, per participant, per channel (i.e. a 19 x 64 (x1) matrix)

I've tried using mean, tried using reshape etc but I am really struggling with the scale of the data and picturing how the the four dimensions fit together. As such I can't confidently manipulate the data across the four dimensions so any guidance would be appreciated.

Best Answer

If you're using release R2018b or later, several data analysis functions (including mean) can accept a vector of dimensions over which to operate. See the Release Notes for a list of which functions can accept a vector of dimensions.

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MATLAB: Average sections of matrix

I am not certain that I understand the result you want.

Try this:

M = rand(31, 109);                                          % Original Matrix
Cols = [ones(1, fix(size(M,2)/25))*25 rem(size(M,2),25)];   % Create Column Sub-Sections 
C = mat2cell(M, size(M,1), Cols);                           % Cell Array Of Sub-Sections
Cmean = cellfun(@(x)mean(x,2), C, 'Uni',0);                 % Row Means For Each Section
Mmean = cell2mat(Cmean);                                    % Convert To Double Matrix Of Row Mean Vectors For Each Sub-Section

MATLAB: Watermark Embedding in Blocks

I think that in some places you mean "pixels", but that possibly in other places you do mean "blocks". Could you go back over your wording and check it?

Your current code is equivalent to the loop-less

Block2 = Block2 + aa * repmat(Block5(:,:,1:64),1,1,64))

but I am not clear as to what your target is.

Best Answer

Related Solutions

MATLAB: Average sections of matrix

MATLAB: Watermark Embedding in Blocks

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