st: row wise summation in panel data for particular IDs

[pb2442@columbia.edu]

Dear all,

I am required to take into account the changes in boundary of cities  
over a period so that all the information can be attributed to the  
parent cities at the start of the time period. I have already tried  
but could not find a similar case in previous threads.
This is a panel data , say with id, year and vars. I need to merge
(sum or weighted sum) two particular ids completely to form a new one.
For instance, I have:

id	year	var1   var2   var3
1	2001	40
1	2002	50
1	2003	60
2	2001	400
2	2002	500
2	2003	600
3	2001	4000
3	2002	5000
3	2003	6000


desired Output will be like (summing up corresponding values of var1  
in given year for id 1 and 2, keeping 3 intact and having the results  
in a newly created id, say 4).
id	year	var1     var2   var3
1	2001	40
1	2002	50
1	2003	60
2	2001	400
2	2002	500
2	2003	600
3	2001	4000
3	2002	5000
3	2003	6000
4	2001	440
4	2002	550
4	2003	660

Any help will be appreciated.


Thanks.

Prabhat

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