MATLAB: How to concatenate a 3-d matrix to 2-d

3-d matrixindexing

Suppose I have a 3-d matrix A. I want to reshape it to a 2-d matrix B as follow:

B=[A(:,:,1); A(:,:,2); . . .; A(:,:,end)];

Is there some easy way to do it?

Best Answer

Two methods, I'll let you test which one is faster, probably the permute one:

B = reshape(permute(A, [1 3 2]), [], size(A, 2))

B = num2cell(A, [1 2]);
B = vertcat(B{:})

Related Solutions

MATLAB: Efficiently converting a 3d matrix to a 2d matrix

You can permute the 2nd and 3rd dimension before doing the reshape:

 >> C = permute(A,[1 3 2]);
 >> C = reshape(C,[],size(A,2),1)

MATLAB: Concatenate multi dimensional matrix

Your b = cat(1, a(:, :, i)) is incorrect and is just equivalent to b = a(:, :, i). If you were to use a loop you could do it like this:

b = [];
for i = 1:size(a, 3)
  b = [b; a(:, :, 1)];   %which is cat(1, b, a(:, :, i))
end

This would be extremely innefficient and matlab's editor will warn you that you're resizing b on every iteration. The proper way to do it in matlab is:

b = reshape(permute(a, [1 3 2]), [], size(a, 2))

without a loop.

Best Answer

Related Solutions

MATLAB: Efficiently converting a 3d matrix to a 2d matrix

MATLAB: Concatenate multi dimensional matrix

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