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matlabvectorcell-array

How to de-interleave a vector?

How to re-order a vector efficiently? The numbers represent 'frames' in a movie that are sorted in the following order:

a=[1 4 7 2 5 8 3 6 9];

the result should be a cell array with the different streams starting with 1,2 and 3:

b{1}=[1 2 3];
b{2}=[4 5 6];
b{3}=[7 8 9];

Right now I'm using a for loop, but I have a hunch it could be done more efficiently (i.e. less lines of code, less time to run) than a for loop:

for ind=1:3
    b{ind}=a(ind:3:end);
end

The final code has ind=1:30000 instead of ind=1:3; is there a more efficient way to do this?

Solution

  • Reshape a to the required shape and use matrix indexing to access its relevant rows. 

    bmat = reshape(a,k,[]);  %k equals 3 in your example
%bmat(1,:) will be your b{1},   bmat(2,:) --> b{2},   and so on.

    If you really need to convert it to a cell like in your question then use mat2cell as follows:

    b = mat2cell(bmat, ones(k,1));