Jason,
My previous answer was wrong. I missed your the "first year of the
first three year period" condition.
Try this:
egen id = group(seller product)
tsset id year
tsspell value, cond(value>0)
egen count = count(_spell) if _spell > 0 , by(id _spell)
gen byte begin = .
levels id, local(levels)
foreach l of local levels {
replace begin = cond(_seq == 1, ///
cond(_seq[_n+1] > _seq , 1, . ///
) , .) if id == `l' & count == 3
}
drop _* count
For example:
+---------------------------------+
| seller product year value |
|---------------------------------|
| 13 456 1988 0 |
| 13 456 1989 0 |
| 13 456 1990 9 |
| 13 456 1991 0 |
| 13 456 1992 2 |
|---------------------------------|
| 13 456 1993 6 |
| 13 456 1994 7 |
| 14 1 1988 1 |
| 14 1 1989 2 |
| 14 1 1990 3 |
|---------------------------------|
| 14 2 1991 4 |
| 14 2 1992 5 |
| 14 2 1993 0 |
| 14 2 1994 0 |
| 15 1 1989 0 |
|---------------------------------|
| 15 1 1990 1 |
| 15 1 1991 2 |
| 15 1 1992 3 |
+---------------------------------+
. do "C:\DOCUME~1\SCOTT~1.MER\LOCALS~1\Temp\STD07000000.tmp"
+----------------------------------------------+
| seller product year value id begin |
|----------------------------------------------|
| 13 456 1988 0 1 . |
| 13 456 1989 0 1 . |
| 13 456 1990 9 1 . |
| 13 456 1991 0 1 . |
| 13 456 1992 2 1 1 |
| 13 456 1993 6 1 . |
| 13 456 1994 7 1 . |
|----------------------------------------------|
| 14 1 1988 1 2 1 |
| 14 1 1989 2 2 . |
| 14 1 1990 3 2 . |
|----------------------------------------------|
| 14 2 1991 4 3 . |
| 14 2 1992 5 3 . |
| 14 2 1993 0 3 . |
| 14 2 1994 0 3 . |
|----------------------------------------------|
| 15 1 1989 0 4 . |
| 15 1 1990 1 4 1 |
| 15 1 1991 2 4 . |
| 15 1 1992 3 4 . |
+----------------------------------------------+
Hope this helps,
Scott
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