When do we use this formula?
In fact, there are many cases need to use this formula to solve the problem!
Suppose you have a row contains day have the event, and you want to count how many events on Monday!
Try to use:
The result is 2, 1 is Monday.
We have general formula:
- dates are range that has to contain weekday.
- day_num is numbered 1-7 for the days Monday-Sunday