Using the Mod Function to Turn a Vector (i.e. 1:15) into [1, 2, 3, 1, 2, 3, 1, 2, 3] etc.

I'm currently reading through the book MATLAB for Clinical and Cognitive Scientists by Mike Cohen. In the book, he mentions a 'neat trick' to covert some vector of linearly-spaced numbers (my e.g. 1:15) into a vector of numbers counting up from 1 to N over and over, using the mod function. This is supposed to work for any arbitrary number n (obviously as we leave greater remainder until we reach the number).

For some reason I just cannot implement what he has suggested. All I can think to do is

mod(startVector, 3)

but obviously the remainder of 3 and 3 is 0, so I end up with [1, 2, 0, 1, 2, 0] etc.

It isn't very necessary, I'm just a little confused that he mentioned something so simple like this that I can't fathom a way to implement. Could anyone help me with this simple problem please?

Answer 1

[JESUS DAVID ARIZA ROYETH]

n=3;
k=[n 1:n-1];
answer=k(mod(1:15,n)+1)

Answer 2

[per isakson]

Or

%%
startVector = 1:15;
vec = mod( startVector, 3 );
vec(vec==0)=3    % replace all zeros by 3
vec =
  Columns 1 through 14
     1     2     3     1     2     3     1     2     3     1     2     3     1     2
  Column 15
     3

Answer 3

[Walter Roberson]

startVector = 1:15;
vec = mod(startVector - 1, 3) + 1;

Answer 4

[Image Analyst]

Yeah, you could do it like that, though a much more straightforward way is to simply use repmat

n = 5; % Whatever you want
out = repmat(1:3, [1, n])    % Replicate [1, 2, 3] five times.

However with the above code, n must be an integer whereas your trick can have a non-integer multiple of n, in case that might be needed.