How to find period of a vector in MATLAB?

Question

By the period I mean this :

Say I have a vector

v = [1,1,1 , 2,2,2 , 3,3,3];
period(v)

ans = 3

This vector should return 3 since the value changes in every 3rd item.

I can simply return the first index where the value changes, but I'm wondering if there is a built-in function, preferrably also working with non-uniform input. i.e. the last sequence could be smaller than 3.

The closest thing I could find is seqperiod but it returns 9 (the length) for this vector.

Thanks for any help!

Answer 1

If you know that the period remains constant for the entire array, you could use the diff() function and pull out the location of the first value like this:

>> diff_out = find(diff(v));
>> diff_out(1)

    ans =
    3

Alternatively, if the period varies, you could run an additional diff to get a vector that represents number of elements between changes like so:

>> diff([0,find(diff(v))])
   ans =

   3     3