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Re: st: Fixing the value in egen command


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Fixing the value in egen command
Date   Tue, 23 Dec 2008 14:51:26 +0000 (GMT)

---  Maarten buis wrote:
> > bys country (year): gen initgdp = gdp[_n==1]
> > bys country (year): replace initgdp = sum(initgdp)

--- Choudry T Shehzad <C.T.Shehzad@rug.nl> wrote:
<snip>
> When I use your command
> 
> bys country (year): gen initgdp = gdp[_n==1980]
> bys country (year): replace initgdp = sum(initgdp)
> 
> all values of initgdp become zeros

_n refers to the observation number and not to the value a variable may
take. So, the first observation is _n == 1 and not _n == 1980 (which is
the 1980th observation, which is missing, and -sum()- treats missings
as zeros, which is why you ended up with all zeros). 

-- 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 N515

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------


      
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