# How to call a function over a rolling window of data?

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Neha Verma on 13 Aug 2022
Commented: Neha Verma on 13 Aug 2022
I have a panel dataset with T=80 and N=23. I want to call a function over the rolling window of data with 20 periods in each window. Simply put, I want MATLAB to read my data as a numeric matrix (T*N). Pick the first 20 observations (T=1 to T=20), estimate the model and save the results. Then, pick up data over a rolling window (T=2 to T=21, T=3 to T=22... and so on), estimate the models and save results. So, the model will be estimated 64 times with 64 result matrices. How do I create the loop for this operation?
Thank you!

John D'Errico on 13 Aug 2022
Edited: John D'Errico on 13 Aug 2022
Yes, there are more sophisticated ways to do this. But for gods sake, why not just write a loop?
You don't say what size the result is. It could be scalar, or a matrix. regardless, just stuff it into something of the proper size.
result = zeros(1,64);
for t = 1:64
T = t + (0:19);
result(t) = fun(obs(T));
end
You don't need anything fancy here.
COULD you do it differently? Of course. For example, you COULD treate a matrix of indices. Somcething like
ind = (1:64)' + (0:19);
Now each row of that matrix is a rolling window of indices. But this is also wild overkill, if you will then loop over the rows of ind.
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Neha Verma on 13 Aug 2022
Thank you, John! My result is in the form of a matrix. Wrote a loop as you suggested. It worked.