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RE: st: forvalues and _N


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: forvalues and _N
Date   Fri, 10 Oct 2008 19:11:13 +0100

I think what Michael wants to know is documented better at -help macro-.


`=exp' where exp is an expression lets you evaluate an expression on the
fly and use its result. 

`=2 + 2' would be in these terms: the expression is 2 + 2; Stata would
evaluate that; and the command would see 4. 

As the example implies, the expression can be a single item such as _N. 

This has been in Stata since (I think) sometime during Stata 7 but was
not documented until Stata 8. There is a discussion within 

SJ-3-2  pr0009  . . . . . . . . . . . . . Speaking Stata:  Problems with
lists
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N.
J. Cox
        Q2/03   SJ 3(2):185--202                                 (no
commands)
        discusses ways of working through lists held in macros

which is visible under the 3-year rule. 

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

P.S. The help and the manuals are, as always, the first documentation to
think of. Typically, the FAQs fill in some odd gaps or fill out some
tricky topics. 

Martin Weiss

see -help _variables-. The equal sign evaluates this -expression- so no
need 
for any -macro-...

Michael I. Lichter

> Whoa! This works even though `=_N' is clearly not a macro. Is this an 
> undocumented feature, or is it a "real" part of Stata that will stick 
> around? I'm sorry if this is discussed somewhere in the FAQ -- I have
no 
> idea how to search for it.

Philip Ryan wrote:
>> Try:
>>
>> forvalues i = 1/`=_N'  {
>>
>> ....
>>
>> }
>>

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