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Re: st: forvalues and _N


From   "Martin Weiss" <martin.weiss1@gmx.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   Re: st: forvalues and _N
Date   Fri, 10 Oct 2008 21:56:08 +0200

"which I know is one of those things you're not supposed to talk about on Statalist."

It has triggered lively debates in the past and there is no explicit prohibition to ask this question, but the economics are such that it (the pdf release) is just not going to happen. And frankly, I have found that the manuals are so good they are worth every one of the admittedly many pennies you spend on them...

HTH
Martin
_______________________
----- Original Message ----- From: "Michael I. Lichter" <mlichter@buffalo.edu>
To: <statalist@hsphsun2.harvard.edu>
Sent: Friday, October 10, 2008 9:02 PM
Subject: Re: st: forvalues and _N


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. 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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--
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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