I am right now trying to generate annual return volatility for each company using the following formula with the monthly returns. My data contains a single number for all months of a given year for each firm. In the formula y stands for year and m stands for month and i stands for a firm. The units for vola are percentage points. I am not sure how to get to an annual return per company, should I use a loop? I don't even have a clue how to start
Attached is my provided data, where I already generated the company_id for each company, monthly returns are given by ret, and risk-free rate (rf) = rf
How to begin? how do I not double count, how to use an efficient way to get the annual return for each company even though the data is monthly? jeeeesus...

Thank you so so so much for your help!!! Best
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