Re: st: St: Programming question, local macros

[Nick Winter <nw53@cornell.edu>]

This comes up periodically.  You can get the same behavior this way:

  . di -4^2
  -16

What's happening is that Stata is evaluating your expression according to 
its order of operations: first the exponentiation, then the subtraction.

It does the same thing when you are using the macro: first substitutes the 
contents of the macro, so "`x'^2" becomes "-4^2" and then "-4^2" is 
evaluated as above.

Remember, Stata's doesn't look at the macro reference `x' and say "aha, 
here is a number," it just blindly substitutes the string -4 for `x' and 
goes on.  (Of course, this is one of the reasons macros are so powerful.)

So in general you want to do something like:

 local xsq = (`x')^2

  . local x = -4
  . local xsq = (`x')^2
  . di `xsq'
  16

--Nick Winter



At 08:37 AM 9/22/2004 -0500, you wrote:

> Could someone please explain the following behavior?  I'm running fully
> up to date Stata 8.2 on Windows 2000.
>
> In a program I have the following statements (with responses
> interspersed):
>
> . local x = -4
> . display `x'
> -4
> . local xsq=`x'^2
> . disp `xsq'
> -16
>
> I kind of expected xsq to have the value of 16 rather than -16.
>
> Thanks in advance.
> --
> Dale Plummer
> Department of Biostatistics
> Vanderbilt School of Medicine
> S-2323 Medical Center North
> Nashville, Tennessee 37232-2158
>
>
> *
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--------------------------------------------------------
Nicholas Winter                           607.255.8819 t
Assistant Professor                       607.255.4530 f
Department of Government              nw53@cornell.edu e
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Cornell University
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*
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