time variable not set r(111); - Calculating Revenue Growth

[Niklas Freudenstein]

Hello everyone, I am trying to calculate revenue growth using the following expression.
. bysort isin year: generate sgrowth = (NET_REVENUES_int / l.NET_REVENUES_int - 1) * 100
Anyone an idea how I can solve the issue regarding the the time variable.
I have multiply entire per company, however the Revenue in each entry is always the same.

[Carlo Lazzaro]

Niklas:
welcome to this forum.
This is not a profitabe way to pose your question.
Please, see the FAQ. Thanks.
That said, see -help tsset-.

[Nick Cox]

Perhaps

tsset isin year 
generate sgrowth = (NET_REVENUES_int / l.NET_REVENUES_int - 1) * 100