Repeated Numbering

Hi there,

I have a dataset with data logs every 30 minutes for 10 years. The columns that I have are 'Year', 'Month', ' Day', 'Hour', 'Minute'. However, I would like them to be classified into a 'Day of Year' column that I will be creating on my own.

Under this new column, I have been able to drag down 48 rows (48 x 30 mins = 24hrs) to select an entire day and, for example, indicate day 1. And then subsequently do the same for the rest of the days, but this is extremely tedious.

I am sure there must be a faster, more efficient way to do this?

I have attached a screenshot of my spreadsheet to make things clearer!

I would appreciate any help at all! Thank you! =)