MATLAB: Re-arranging array columns in alternating form

alternating columnsreshaping arrays

I would like to write a function: 
function [Y]=AlternateColumns(X,n)
that takes an array X of the form:
AlterBefore.png
and turns it into Y of the form:
AlterAfter.png
In this example n=3, but it could be any number by which the entire number of columns is divisible. How is this possible without using a loop?

Best Answer

function Y = AlternateColumns(X, n)
    Y = reshape(permute(reshape(X, size(X, 1), [], n), [1 3 2]), size(X, 1), []);
end
Basically, reshape into a 3D array, swap dimensions 2 and 3 and reshape back into original shape.
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