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st: AW: AW: generate new variable from differencing where subtracted variable is fixed


From   "Martin Weiss" <martin.weiss1@gmx.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: AW: AW: generate new variable from differencing where subtracted variable is fixed
Date   Fri, 5 Mar 2010 17:32:39 +0100

<> 


Disassemble this into separate processes if you want to:

*************
clear*

inp int year byte(x1 x2)  
1960 5 8      
1960 4 10     
1960 2 3       
1961 5 7       
1961 1 2        
1961 3 5
end

//get first value per year into new var
//use -bysort- here as in NJC`s
//http://www.stata-journal.com/sjpdf.html?articlenum=pr0004
bys year: gen byte x2_1=x2[1]

//form diffs
gen byte diff=x1-x2_1

list, noo sepby(year)
*************

You first use -bysort- to have Stata interpret any subscripts as within the
groups fed as a -varlist- to -bysort-. See NJC´s article cited in the code.
The result is year-specific, so the next step can afford to omit the
-bysort-, and take the difference unconditionally...


HTH
Martin


-----Ursprüngliche Nachricht-----
Von: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] Im Auftrag von Martin Weiss
Gesendet: Freitag, 5. März 2010 17:23
An: statalist@hsphsun2.harvard.edu
Betreff: st: AW: generate new variable from differencing where subtracted
variable is fixed


<> 



*************
clear*

inp int year byte(x1 x2)  
1960   5     8          
1960   4     10         
1960   2     3          
1961   5     7          
1961   1     2          
1961   3     5          

end


bys year: gen diff=x1-x2[1]

list, noo
*************



HTH
Martin


-----Ursprüngliche Nachricht-----
Von: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] Im Auftrag von Johannes
Schoder
Gesendet: Freitag, 5. März 2010 17:00
An: statalist@hsphsun2.harvard.edu
Betreff: st: generate new variable from differencing where subtracted
variable is fixed

Dear Statalist users:

I try to calculate the difference between two variables for a panel data 
set, where the subtracted variable (here x2) is always the first 
observation of each year:
For example:
Year   x1   x2         difference: x1-x2 if x2 is the first obs. of the year

1960   5     8           5-8
1960   4     10         4-8
1960   2     3           2-8
1961   5     7           5-7
1961   1     2           1-7
1961   3     5           3-7


I tried something like: bysort year: gen difference= x1-x2[_n==1] but 
Stata does only calculate the first observation for each year and 
otherwise generates missings.
Thanks a lot for any hint!
Regards,
Johannes

-- 


Johannes Schoder
Socioeconomic Institute
University of Zurich
Hottingerstr. 10
8032 Zurich

Phone: +41 44 634 0612
Fax:   +41 44 634 4987
E-mail: johannes.schoder@soi.uzh.ch

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