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st: RE: Evaluating an expression in -forvalues-


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Evaluating an expression in -forvalues-
Date   Tue, 16 Dec 2003 10:14:16 -0000

You can get evaluation on the fly with `=exp' 
where "exp" is an expression to be evaluated. 
That expression can itself include local macros.
So 

forval i = 1(1)`=`t'+2' { 
	...
} 

or 

forval i = 1/`=`t'+2' { 
	...
} 

Note that this is nothing to do with -forvalues- 
as such. It is a general device for handling 
macro evaluation, added in Stata 7 (but not documented) 
and documented in Stata 8. For example, start at the 
on-line help for -macro-. 

There was also related discussion within SJ 3(2):185--202
(2003). 

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

Richard Upward
 
> I'm trying to write some code that repeats a varying number 
> of times, based on an argument `t'.  I'd like to be able to 
> write, for example
> 
> forvalues i = 1(1)`t'+2 {
>                <some code>
>                }
> 
> but -forvalues- does not seem to allow this because it 
> evaluates `t' but does not add it to the 2.  So, if `t' was 
> 10 I end up with
> 
> forvalues i=1(1)10+2
> 
> which gives a syntax error.  Is there a way to force 
> -forvalues- to evaluate an expression like this, or do I 
> need to set another macro equal to `t'+2 before the loop?  
> That seems a bit clunky.  I noticed that I can use an 
> expression like this in a -while- loop.

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