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Re: st: forvalues and _N


From   "Michael I. Lichter" <mlichter@buffalo.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: forvalues and _N
Date   Mon, 13 Oct 2008 10:09:15 -0400

Thanks for the reference to the article, Nick; I didn't realize that it 
was available for free, so I didn't go looking for it. (My library 
doesn't subscribe to STB or SJ and, given the state budget situation, I 
don't think that's going to change.)

As for the help being terse, that's for certain!

Michael

Nick Cox wrote:
> The help _is_ complete on this question, just terse. 
> 
> The affordability of the manuals remains a separate issue, although no
> doubt it bites hard. I can't add to many earlier comments on this issue.
> But there is no taboo on talking about this on the list. It's just the
> same question will get the same answers! 
> 
> One of the forms that 
> 
> expansion_optr 
> 
> can take is listed as 
> 
> = exp
> 
> and links take you to other entries for Stata's language, including exp
> as indicating an expression. 
> 
> Michael also overlooked my point that a relevant tutorial exists with no
> marginal cost to him. 
> 
> Nick 
> n.j.cox@durham.ac.uk 
> 
> Michael I. Lichter
> 
> Thanks Nick and Martin, although I don't see this in either -help macro-
> 
> or -help variables- ... unless it's the uninterpretable (to me)
> 
> 	"[...] `expansion_optr' [...]"
> 
> in -help macro- (FYI: Stata 9.2). I'm guessing that it IS in [P] Macro, 
> but I frankly can't afford the manuals and wish Stata would make them 
> available free online like SAS or on the install DVD like SPSS or at a 
> reasonable price in PDF form online which I know is one of those things 
> you're not supposed to talk about on Statalist. Grrr.
> 
> Michael
> 
> Nick Cox wrote:
> 
>> 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. 
>  
>  
>> 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'  {
>>>>
>>>> ....
>>>>
>>>> }
>>>>
>> *
>> *   For searches and help try:
>> *   http://www.stata.com/help.cgi?search
>> *   http://www.stata.com/support/statalist/faq
>> *   http://www.ats.ucla.edu/stat/stata/
> 

-- 
Michael I. Lichter, Ph.D.
Research Assistant Professor & NRSA Fellow
UB Department of Family Medicine / Primary Care Research Institute
UB Clinical Center, 462 Grider Street, Buffalo, NY 14215
Office: CC 125 / Phone: 716-898-4751 / E-Mail: mlichter@buffalo.edu

*
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*   http://www.ats.ucla.edu/stat/stata/



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