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st: RE: Mixing global macros with local macros


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Mixing global macros with local macros
Date   Wed, 9 Oct 2002 16:50:48 +0100

mganz
> 
> I'm running Stata 6.0 and I want to set some global 
> macros in one program and then access them, in a 
> general way in another.
> 
> This is what I want to do:
> 
> * In the main program I set the globals
> global skip1=1
> for num 2/10: global skipX=0
> do something

This can slow a program down. -while- is 
going to be faster than -for- for this. 
(In 7, -forval- is even faster and better.) 

> 
> * Then in the something.do file I want to repeatedly
> * do some regressions and simulations, but only if
> * a $skip macro is not equal to 1
> local i=1
> while (`i'<=10){
> 	if $skip`i'~=1{
> 		reg y x w z, if b==`i'
> 		* etc, etc
> 	}
> 	local i=`i'+1
> }
> 
> But when the while-loop expands the $skip`i' it doesn't 
> expand it to $skip1, $skip2, etc.
> 
> How can I accomplish this in a generalized and hopefully
> not too cumbersome way?

The problem is that Stata is reading from left 
to right and dividing your command into tokens. 
By default the ` of `i' is taken as a signal 
that a new token is starting, and so necessarily 
that current token, which started with $skip,
is ending. Thus Stata treats your line as 

$skip 

followed immediately by 

`i' 

Very likely, $skip is undefined and so 
evaluates to an empty string. `i' is 
of course well defined. 

You just have to flag to Stata to substitute `i' 
before it works out the global: 

${skip`i'} 

That way, Stata does things in the right order, 
just as with parentheses, brackets and braces
in an algebraic expression, except that Stata
uses braces for this specific purpose. 

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