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Re: st: programming: exiting nested loops


From   Joseph Coveney <jcoveney@bigplanet.com>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   Re: st: programming: exiting nested loops
Date   Fri, 30 Mar 2007 22:53:01 +0900

Laura Gibbons wrote:

I'm writing a simulation program where if something happens, I want to
jump out of a set of nested loops and go to the next replication.  Is
there a short cut for putting -continue, break- in every nested loop?

When I learned Fortran with numbered program lines (cards, actually, this
was 36 years ago!), I could just write "GO TO 100" which meant go to line
100.  Is there anything similar in Stata?

--------------------------------------------------------------------------------

You can place the nested loops into a subprogram that is called by your
simulation program.  Note that, if you use -forvalues- or -foreach- (as
opposed to -while-) for the loops in the satellite program, then you must
throw an exception in order to terminate early:  see
www.stata.com/statalist/archive/2006-10/msg01186.html .

You might be able to use -while- loops that test two conditions (loop
counter & breakout-flag status) in your main simulation program and avoid
using a subprogram altogether.  -while- might be a little slow for use in
nested loops inside a program called by -simulate-, however.  My
understanding is that -forvalues- and -foreach- are faster.

If you can invest the time up-front, Mata is an alternative that might be
fastest in execution.  And you can code -if (something == happens) goto
L100- in it, although another style might prove better.

Joseph Coveney

program define mysimulation, rclass
   version 9.2
   .
   .
   .
   tempname A
   local count . . .
   matrix define `A' = . . .
   .
   .
   .
   capture mynesteddoloops , inputarg(`count') ///
     resultarg(`A')
   if (_rc == -1) {
       .
       .
       .
   }
   else if (_rc == 0) {
       .
       .
       .
   }
   else exit = _rc
   .
   .
   .
end
*
program define mynesteddoloops
   version 9.2
   syntax , inputarg(integer) resultarg(name)
   .
   .
   .
   forvalues i = 2/`inputarg' {
       forvalues j = 1/`=`i'-1' {
           if (. . .) exit = -1
           matrix define `resultarg'[`i',`j'] = . . .
           .
           .
           .
       }
   }
end
*
simulate . . . : mysimulation . . .
exit

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