matlab making repetitions of data from one array into another array

Question

I would appreaciate a lot if you help. I am beginner in programming. I am using Matlab. So, I have an array which is 431x1 type - double; there i have numbers 1 to 6; for ex: 1 4 5 3 2 6 6 3 3 5 4 1 ...; what I want to do is I need to make a new array where I would have each element repeat for 11 times; for ex: a(1:11)=1; a(12:22)=4; a(23:33)=5; or to illustrate differently : a=[1 1 1 1 1 1 1 1 1 1 1 4 4 4 4 4 4 4 4...]; I tried doing it in a loop but had some problems, which way could you suggest, do you know any function I could take advantage of?

Answer 1

First of all, it would help if you could format your code is separate blocks to make your question easier to read...

---

Let's say you had an array of length Nx1 as:

x = [1 2 3 4 5 ...]';

You could construct a loop and concatenate as:

for i = 1 : length(x)

for i = 1: length(x)
    y(1 + (i - 1) * 11 : 1 + i * 11) = x(i);    % Copy to a moving block
end
y(end) = [];    % Delete the superfluous one at the end

You could also look at functions like repmat in the MATLAB help for replicating arrays.

Answer 2

Try this (NRepis how many times you want it repeated):

 x = [1, 2, 3, 4, 5];
 NRep = 5;
 y = reshape(repmat(x,[NRep,1]),[1,length(x)*NRep])

Since it's a little cumbersome to write that out, I also particularly enjoy to use this "hack":

 x = [1, 2, 3, 4, 5];
 NRep = 5;
 y = kron(x, ones(1,NRep));

Hope that helps!

P.S.: This is designed for row vectors only. Though if you need column vectors it's easy to modify.

edit: Of course, if you're post-R2015a you can just use y=repelem(x,NRep). I tend to forget about those because I work on older Matlabs (and sometimes it's not such a bad idea to be a bit backward compatible). Thanks to @rahnema1 for reminding me.