Re: st: How can I find the sum of specific values of a variable?

[David Kantor <dkantor@jhu.edu>]

At 09:39 PM 11/20/2003 +0000, A Delis wrote:
> Dear Statalisters
>
> I have a dataset like the following, where the SIC values are in an 
> ascending order
> SIC     EXP
> 2011    667.8039
> 2013    130.8002
> .
> .
> .
> .
>
> 2095    38.90306
> 2098    0.617763
> 2111    249.92
> 2121    3.738577
> 2131    35.32281
> .
> .
> .
> 2298    5.709858
> 2299    39.7519
> .
> .
> etc
>
> What I want to find is the sum of EXP values that have a SIC value 
> begining with 20, i.e. 667.8039+130.8002+..+38.90306+0.617763
> In others words I have some 4digit SIC data and I want to aggregate them 
> into  2digit SIC.
You did not indicate the type of SIC.  I will assume it is numeric.

 gen byte sic_1 = int(SIC/100)

(If SIC is string, you will need to so something analogous, using substr().)


Then you aggregate by sic_1, i.e.,

 egen  mysum = sum(EXP), by(sic_1)

or you might want to -collapse- the data instead:

 collapse (sum) EXP, by(sic_1)

Note that egen..sum will retain the original form of the data, generating a 
constant value within each distinct value of sic_1.  -collapse- will shrink 
the data to one observation per distinct value of sic_1.

I hope this helps.
-- David.


David Kantor
Institute for Policy Studies
Johns Hopkins University
dkantor@jhu.edu
410-516-5404

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