-- Nick wrote:
> If the argument is not a variable in the dataset, the return code
> from -confirm- will be positive, and if it is, the return code will
be
> zero. So,
>
> !_rc
>
> is non-zero if it's present and zero otherwise. So Maarten's second
> example does not read quite correctly.
The code is a bit cryptic, but it is correct. In my code !_rc should
return false if the the variable is absent. The ! negates the statement
following it: _rc. In Stata 0 is false and any positive number is true,
so if the variable is absent _rc will contain a positive number (true)
and ! negates it and turns it into false (0). If the variable is
present than _rc contains false (0) and ! negates it and turns it into
true. The way you can make sense of this code is to read -if !_rc- as
"if no problem".
*----------- begin example ------------
sysuse auto, clear
capture confirm variable price
if !_rc {
di "price is pressent"
}
sysuse nlsw88, clear
capture confirm variable price
if !_rc {
di "price is present"
}
*------------ end example -------------
(For more on how to use examples I sent to the Statalist, see
http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )
Hope this helps,
Maarten
-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands
visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434
+31 20 5986715
http://home.fsw.vu.nl/m.buis/
-----------------------------------------
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