Thomas Speidel wrote:
I am trying to tag the first non-zero, non-missing observation within a
variable by group. The goal is to drop anything BEFORE the expression
is measured within a group. For example:
group time expression
1 1 0
1 2 0
1 3 3.2
1 4 4.1
1 5 0
1 6 2.5
2 1 0
2 2 .
2 3 0
2 4 3.7
2 5 4.0
..
My goal is to obtain this:
group time expression
1 3 3.2
1 4 4.1
1 5 0
1 6 2.5
2 4 3.7
2 5 4.0
..
-------------------------------------------------------
Doesn't this do what you want?
sort group time
by group: gen x=sum(expression)
keep if x>0
This requires that -expression- can not be negative. If that could happen, you should create a help variable being 1 when -expression- is neither zero nor missing:
gen z = expression!=0 & expression<.
by group: gen x=sum(z)
keep if x>0
Hope this helps
Svend
________________________________________________________
Svend Juul
Institut for Folkesundhed, Afdeling for Epidemiologi
(Institute of Public Health, Department of Epidemiology)
Vennelyst Boulevard 6
DK-8000 Aarhus C, Denmark
Phone, work: +45 8942 6090
Phone, home: +45 8693 7796
Fax: +45 8613 1580
E-mail: [email protected]
_________________________________________________________
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