sliding window from column value

I have a 7000x10 matrix, with one of the column being the years from 1985 to 2019. I want to make a sliding window which will go over a 5 years width with a 1 year step size. My problem is that every year holds a different number of events, which means that I can't use a fixed width like I saw with other sliding window techniques.

[Walter Roberson]

In your particular case, could it help to pre-calculate summary information by year?