Perhaps it is bad that I didn’t know this before, but the following code for Stata would have saved a week off of my dissertation work. Suppose that you have data structured like so:
and you want to create a new variable that is the total amount as of each date for each firm. In Stata, you simply type:
sort firm_id date
bysort firm_id: gen total_t = sum(amount)
Note the use of ‘gen‘ rather than ‘egen.’ The ‘sum’ command differs by the type of generate command (i.e. gen or egen), so about 500 lines of loops written in Stata code could be condensed in a few lines. Stata needs to fix the ‘egen’ and ‘gen’ distinction or I need to port more of my projects to R.