Repetition of array elements in MATLAB

Question

I have a MATLAB array and want to make a repetition based on the number of array elements. Below is the example that I want.

a = [2, 4, 6, 8]

If I want 7 elements, the result is

aa = [2, 4, 6, 8, 2, 4, 6]

Or if I want 5 elements,

aa = [2, 4, 6, 8, 2]

Is there any MATLAB function which makes these kind of result?

Answer 1

You can use "modular indexing":

a = [2, 4, 6, 8]; % data vector
n = 7; % desired number of elements
aa = a(mod(0:n-1, numel(a))+1);

Answer 2

One simple option will be to use a temporary variable for that:

a = [2 4 6 8];
k = 7;
tmp = repmat(a,1,ceil(k/numel(a)));
aa = tmp(1:k)

First, you repeat the vector using the smallest integer that makes the result larger than k, and then you remove the excess elements.

If you do that many times you can write a small helper function to do that:

function out = semi_repmat(arr,k)
tmp = repmat(arr,1,ceil(k/numel(arr)));
out = tmp(1:k);
end