Bysort Trouble

[Erik Tiersten-Nyman]

Hello,

I am attempting to execute a very simple command where I create a new variable for each id (appearing many times in my data) corresponding to the first year that id appears in the data. My code is as follows:

bysort id: egen(first_year)=min(year)

Year is a numerical variable. However, I am getting the error "( invalid name, r;198". I have run similar commands in Stata countless times without any issues, so I am not sure what the problem is.

I also tried
by id: egen(first_year)=min(year)
but was met with the same error.

Any ideas?

Thanks in advance,

Erik

[Sarah Edgington]

Stata is objecting to you specifying a variable name in parentheses.

Try

 bysort id: egen first_year=min(year)

[William Lisowski]

Note that you can simplify your code.

bysort id (year): generate first_year = year[1]

The data will be sorted by id and within each id by year, then for each id the variable first_year will be set to the value of year in the first observation for that id, which will be the observation with the smallest value of year.