Hi,
I have this type of table in Stata:
industry_id period_1 period_2 sales_1 sales_2
11 1 0 100 .
11 0 1 . 200
12 1 1 50 60
13 1 0 40 .
I am looking to convert it to this table:
industry_id period sales
11 1 100
11 2 200
12 1 50
12 2 60
13 1 40
Please help.

Thank you.
Olga