st: calculating age / tenure

["Ravindran, Kiron" <kiron.r@gmail.com>]

I know there should be a simple way of doing this. But am tying myself
up in knots figuring this out. Perhaps someone here can help

I have a table that looks like this Company1, Company2, Year of alliance

I want to calculate three different measures.
1. Company 1's experience: i.e. Year of Alliance of the Company1 minus
the first Year of Alliance of company 1. (this captures the number of
years of experience Company 1 has by being in any alliance)

2. The same for company 2

3. The alliance experience. The current year of alliance minus the
year of alliance when this particular dyad of Company 1 and Company 2
had their first alliance

Thanks in advance
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