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st: RE: RE: RE: RE: Parsing not-quite-standard syntax


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: RE: RE: Parsing not-quite-standard syntax
Date   Fri, 26 Nov 2004 17:34:08 -0000

No, that first route is unnecessary. How about 

program foo
	gettoken data 0 : 0, parse(",") 
	syntax [, * ]  
	use `data', clear 
	count 
	...
end 

That way, any -if- or -in- are just bundled within `data'. 

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

> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Nick Cox
> Sent: 26 November 2004 16:19
> To: statalist@hsphsun2.harvard.edu
> Subject: st: RE: RE: RE: Parsing not-quite-standard syntax
> 
> 
> That's much clearer to me now. You've discovered that 
> -if- and -in- are checked for consistency with the 
> data in memory. There seem to be two routes to follow. 
> 
> -gettoken- can look for -if- and pick up what follows. 
> But that could be several tokens e.g. 
> 
> if foo > 20 & bar < 10 
> 
> so you have to keep going until you find an -in- 
> or a comma. And vice versa. 
> 
> You read it your dataset and then process the 
> other stuff. Say 
> 
> gettoken data 0 : 0 
> use `data', clear 
> syntax [if] [in] [, * ] 
> marksample `touse' 
> keep if `touse' 
> ... 
> 
> Nick 
> n.j.cox@durham.ac.uk 
> 
> David Harrison
> > 
> > You say 'Stata isn't good at extra-sensory perception' 
> > however the command -use- can manage it...
> > 
> > . clear
> > 
> > . use auto.dta if foreign==1
> > (1978 Automobile Data)
> > 
> > . tab foreign
> > 
> >    Car type |      Freq.     Percent        Cum.
> > ------------+-----------------------------------
> >     Foreign |         22      100.00      100.00
> > ------------+-----------------------------------
> >       Total |         22      100.00
> > 
> > . clear
> > 
> > . use auto.dta in 1/10
> > (1978 Automobile Data)
> > 
> > . count
> >    10
> > 
> > The syntax looks standard, but cannot be parsed by the 
> > -syntax- command. Suppose the program I wanted to write was 
> > as follows (in reality it is more complex, obviously)...
> > 
> > program foo
> > 	syntax [name] [if] [in] [, *]
> > 	use `namelist'.dta `if' `in' , `options'
> > end
> > 
> > Then...
> > 
> > . clear
> > 
> > . foo auto if foreign==1
> > foreign not found
> > r(111);
> > 
> > . foo auto in 1/10
> > Obs. nos. out of range
> > r(198);
> > 
> > So what I am trying to work out is how to manually parse the 
> > input (using -gettoken- and the like) to identify the name 
> > (if there is one), if statement (if there is one), in 
> > statement (if there is one) and options (if any are specified).
> > 
> > I could get around it by putting the [if] and [in] as options 
> > instead, eg
> > 
> > syntax [name] [, ifopt(string) inopt(string) *]
> > 
> > but this goes against the appeal of the intuitive standard 
> > syntax of Stata, so I wondered if anyone had overcome this 
> > problem before?
> > 
> > David
> > david@icnarc.org
> > 
> > Nick Cox
> > 
> > > I don't however understand the bit about 
> > > variables not in memory. Stata isn't good 
> > > at extra-sensory perception... 
> > > 
> > > David Harrison
> > >  
> > > > I want to write a command with the syntax
> > > > 
> > > > command [name] [if exp] [in range] [, opt1 opt2 *]
> > > > 
> > > > BUT, the -if exp- and -in range- are to be applied in a -use- 
> > > > statement, so they may involve variables that are not in the 
> > > > dataset in memory. Any suggestions on how I can parse this to 
> > > > get the locals `namelist' `if' `in' `opt1' `opt2' and 
> > > > `options' that would be produced by -syntax-?
> 
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