--- William Bishop <[email protected]> wrote:
> I want to generate a variable by making calculations comparing the
> current observation to ALL the previous observations with the same
> id.
>
> Let's say I want to sum the difference in variable x for the
> observation 5 vs all the previous obs. It would look something like:
>
> gen diffx=(x[5]-x[4])+(x[5]-x[3])+(x[5]-x[2])+(x[5]-x[1])
Here is a solution without resorting to a loop:
*----------------- begin example -------------------
drop _all
input id obs x
1 1 2
1 2 5
1 3 6
1 4 8
1 5 11
2 1 3
2 2 4
2 3 6
2 4 7
2 5 9
2 6 11
end
sort id obs
by id (obs): gen diffx = _n*x - sum(x)
list
*----------------------- end example ------------------
(For more on how to use examples I sent to the Statalist, see
http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )
Hope this helps,
Maarten
-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands
visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434
+31 20 5986715
http://home.fsw.vu.nl/m.buis/
-----------------------------------------
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