st: How to calculate cross-subgroup values within the same variable?

[Yao Amber LI <yaoamber@gmail.com>]

Dear Statalisters,

I am trying to calculate a cumulative distance between each local firm
and all other foreign firms within the same industry each year.

My data structure is as follows (for each year and each industry).

Firm_ID   ownership       latitude       longitude
1          local
2          local
3          local
4          local
5          local
…          local
I           local

1          foreign
2          foreign
3          foreign
…          foreign
J           foreign

To sum up, in each industry each year, I have a group of local firms
with their latitude and longitude; and a group of foreign firms with
their latitude and longitude.
I need to calculate a cumulative distance between each local firm (i)
and all other foreign firms in that industry the same year. The
distance formula will be Dist_i = sum_{j} function(d_{ij}), where
i=1,…, I; and j=1,…, J. And d_{ij} is a function of latitude_{i},
longitude_{i} and all other FOREIGN firms’ latitude and longitude.

How should I achieve that object? How can I loop over each local firm
with all other foreign firms?

Any help would be appreciated. Thanks!


All my best,

Amber

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