How to fill a matrix using elements from another?

Question

I have a matrix:

A = [1;2;3;4];

I would like to create another matrix B of size 20*1 from A. How can I implement that effectively? Elements can be repeated and should be picked in random order.

Answer 1

For the general case, where the elements of A can take any value, you can use randsample (you can even set different probabilities for each element).

B = randsample(A(:),20);

Answer 2

you can use randi for that, for your example:

B = randi(4,20,1)

For the general case where A has other values and other sizes, use indexing:

B = A(randi(numel(A),20,1))