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st: RE: simplifying foreach loop


From   Nick Cox <n.j.cox@durham.ac.uk>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: simplifying foreach loop
Date   Mon, 11 Oct 2010 20:40:57 +0100

Your approach is not going to work for a reason explained to you by Maarten Buis earlier today. 

Consider 

by sic_n, sort: egen datmedian=median(r_d) if sic_n>=2010 &
sic_n<=2019
by sic_n, sort: egen datmedian=median(r_d) if sic_n>=2020 &
sic_n<=2029

Once the first command is completed, the second will fail because the variable -datmedian- already exists, and -egen- needs a new variable to work. 

But you just need a coarsened SIC variable. 

gen sic_n_2 = 10 * floor(sic_n/10) 
egen datmedian = median(r_d), by(sic_n_2) 

No loops at all! 

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

Biljana Dlab

I have firms sorted by SIC from 2000-3999 and would like to compute the
3-digit industry median.

How do I simplify this loop, so that the increment in sic_n are
increasing by 10 without writing out every line?

. foreach v of var r_d {
  2. gen d`v'=.
  3. by sic_n, sort: egen datmedian=median(r_d) if sic_n>=2010 &
sic_n<=2019
  4. by sic_n, sort: egen datmedian=median(r_d) if sic_n>=2020 &
sic_n<=2029
  5. by sic_n, sort: egen datmedian=median(r_d) if sic_n>=2030 &
sic_n<=2039
  6. by sic_n, sort: egen datmedian=median(r_d) if sic_n>=2040 &
sic_n<=2049
  7. by sic_n, sort: egen datmedian=median(r_d) if sic_n>=2050 &
sic_n<=2059
  8. by sic_n, sort: egen datmedian=median(r_d) if sic_n>=2060 &
sic_n<=2069
  9. by sic_n, sort: egen datmedian=median(r_d) if sic_n>=2070 &
sic_n<=2079
(...) 
till
	by sic_n, sort: egen datmedian=median(r_d) if sic_n>3990 &
sic_n<3999
}


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