Egen stands for extensions to generate. It is used for creating new variables, the difference from generate being that egen has a large library of functions to choose from.

For instance, suppose you want to create total_vac as a sum of male_vac, female_vac, and trans_vac. We can do this using gen total_vac = male_vac + female_vac + trans_vac but can also use the rowtotal function of egen: egen total_vac = rowtotal(male_vac female_vac trans_vac). rowtotal has a little pathology related to missing values, though; it treats missing values as zeroes, which often is not the desired outcome. So, be careful about what you want!

You can check out the list of functions in egen in its help file (help egen). Though its introduction might seem a bit disparate, we are covering it today because it is often used with by (or bysort) which is today’s central topic.