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
..
I would like to avoid reshaping the dataset (where the useful "egen
rfirst" would help). I have tried using various subscripting
expressions, but none produced the end result.
bysort group: gen firstexp=1 if expression[_n] > expression[n-1]
bysort group: gen cum=sum(firstexp)
gen tag=firstexp-cum
gen first=tag==0
The above commands gets me one step closer, but it still doesn't get me
there...
Thanks,
Thomas Speidel
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