egen if else max min

[Aurele Major]

Hi everyone,

I wish to write a code that finds the maximum of the variable "difference" if the variable "negpost" is equal to 1, the minimum of the variable "difference" if the variable "negpost" is equal to -1, and just a dot if "difference" is equal to another value than -1 or 1 (see attached file for screenshot of data). This must also be done by "our_director_id" "permno1" and "event_date"

I wrote the following code, but it doesn't seem to work:

if negpost==1 {
by our_director_id permno1 event_date: egen minmax = max(difference)
}
else if negpost==-1 {
by our_director_id permno1 event_date: minmax = min(difference)
}

Would be really great if someone of you could explain me what I'm doing wrong. Thanks a lot.

Aurele

[Nick Cox]

The if statement is not what you need. See

http://www.stata.com/support/faqs/pr...-if-qualifier/

An egen is probably intended in the second long command, but if you start with that idea I don't think you can recast the code easily.

So I think you need something else. Consider

bysort our_director_id permno1 event_date (difference): gen minmax = difference[_N] if negpost == 1
by our_director_id permno1 event_date: replace minmax = difference[1] if negpost == -1

This assumes that (a) negpost is constant within distinct groups of our_director_id permno1 event_date
(b) that difference is never missing

Alternatively, but with assumption (a) only, this should work:

by our_director_id permno1 event_date: egen max = max(difference) if negpost==1
by our_director_id permno1 event_date: egen min = min(difference) if negpost==-1
gen minmax = min(min, max)

[Aurele Major]

This is exactly what I needed! Thanks a bunch!

[Nick Cox]

Good. Now please promise never to use photos of data listings again! http://www.statalist.org/forums/help#stata