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st: RE: Insert new observation by group


From   Nick Cox <n.j.cox@durham.ac.uk>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Insert new observation by group
Date   Wed, 2 Nov 2011 21:25:03 +0000

I don't understand all your requirements. I have 1 + 2 + 2 = 5 (not 6) for group 1 and similarly get a different sum for group 2. 

Also, you don't explain where -ingap- comes from. 

The bit you may be missing most is -expand-. This may give you a start. 

bysort group : gen order = _n 
by group: gen last = _n == _N 
expand 2 if last 
bysort group (order) : replace y = <whatever> if _n == _N 
by group : replace x = <something else> if _n == _N

Nick 
n.j.cox@durham.ac.uk 

Fernando Luco

I'm trying to create a new observation for each group in my data, but
I haven't been able to do so. I tried using -ingap- but didn't work
because
it inserts the new observation at the top of the group or after the
first observation.
My data looks as follows:

group y	 x
1	1	10
1	2	10
1	2	10
2	3	8
2	1	8

What I want is to insert a new observation at the end of each group,
and this observation must be the difference between "x" (in my case
this is 10 for group one and 8 for group two) and the sum of "y"
(6 for group one and 3 for group two). So, the idea is that the final
dataset should look as follows

group y	x
1	1	10
1	2	10
1	2	10
1      5       10
2	3	8
2	1	8
2      4       8

Any ideas? Thanks,

Fernando
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