I have Matrix A with n,n dimensions. How can I replace every second column of A with column vector x (of size n).
I want to do it without any "for/while" loops,
can someone please help me? thanks.
2 Answers
Suppose this is your data:
A = rand(11); V = ones(size(A,1),1); Then this is how you assign the vector to each second column of the matrix:
idx = 2:2:size(A,2) A(:,idx) = repmat(V,numel(idx)) answered Oct 25, 2013 at 10:13
Dennis Jaheruddin
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%// Create example data n = 21 A = magic(n) x = ones(size(A,1),1); %// Replace every second column of A with x starting from the first column m = ceil(size(A, 2)/2); X = x(:, ones(1,m)); %//Replicate x A(:,1:2:end) = X %// Put x in each odd column. If you want it to start from the second column then you must use floor instead of ceil
%//Create example data n = 6 A = magic(n) x = ones(n,1); %// Replace every second column of A with x starting from the second column m = floor(size(A, 2)/2); X = x(:, ones(1,m)); A(:,2:2:end) = X 4 Comments
Rami
the first 3 lines are for creating from X a matrix (n,n)?
Dan
@Rami yes. You only need the last three lines. The first three are just creating example data
Rami
why do I need the x vector to be a matrix? why can't it stay a simple vector?
Dan
@Rami Matlab won't allow you to assign a vector to a matrix. You can assign a scalar to every element of a matrix but not a vector. Matrix assignment needs to be 1 to 1, so you you need to change
x to a matrix X that has columns equal to the number of columns you are assigning to (and the same rows obviously)