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From |
Austin Nichols <austinnichols@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: Obtain the list of variables used in an if condition |

Date |
Thu, 13 Aug 2009 09:57:19 -0400 |

Sergiy et al.-- I wouldn't worry about macros since they will be evaluated, but I am probably missing some other problems. Here was my imperfect first cut: clear all prog shvars syntax [if] tempname x loc if:subinstr loc if "c(" "`x'", all loc if:subinstr loc if "r(" "`x'", all loc if:subinstr loc if "e(" "`x'", all tokenize `"`if'"', parse(" !~^+-*/=<>]()&|") while `"`1'"'!="" { cap unab v: `1' if _rc==0 loc varlist "`varlist' `v'" mac sh } di "`varlist'" end sysuse auto su mpg g meanvar=1 shvars if mpg==r(mean)&(di==_pi|gear_r==c(pi)) Here is one headache: . shvars if mpg==r(mean)&(di==_pi|gear_r==c(pi))&floor(f)==0 mpg displacement gear_ratio . shvars if mpg==r(mean)&(di==_pi|gear_r==c(pi))&trunc(f)==0 mpg displacement gear_ratio . shvars if mpg==r(mean)&(di==_pi|gear_r==c(pi))&reverse(make)=="" mpg displacement gear_ratio I.e. it is not good enough to strip out r( and c( and e( since these can be the end of a function. Here is one fix, but still not complete (no mention of factor variables yet): clear all prog shvars syntax [if] tempname x foreach h in c e r { foreach a in `c(alpha)' { loc if:subinstr loc if "`a'`h'(" "`a'x(", all } loc if:subinstr loc if "`h'(" "`x'", all } tokenize `"`if'"', parse(" !~^+-*/=<>]()&|") while `"`1'"'!="" { cap unab v: `1' if _rc==0 loc varlist "`varlist' `v'" mac sh } di "`varlist'" end sysuse auto su mpg g meanvar=1 shvars if mpg==r(mean)&(di==_pi|gear_r==c(pi)) shvars if mpg==r(mean)&(di==_pi|gear_r==c(pi))&floor(f)==0 On Wed, Aug 12, 2009 at 4:48 PM, Jeph Herrin<junk@spandrel.net> wrote: > Another consideration is that an -if- condition can > refer to a scalar > > ******************** > program foo > syntax [if] > di "`if'" > end > ******************** > . clear, all > . scalar cond=1 > . foo if cond==1 > if cond==1 > > not to mention locals and globals. > > Good luck! > > Jeph > > > > > Nick Cox wrote: >> >> I don't know a neat way to do this. Among other problems, a complete >> solution would need to consider that >> 1. An -if- condition might contain temporary variable names, too. Your >> logic seems to hold despite that. >> 2. An -if- condition could refer to r(), e(), c() and Stata matrices. >> Your logic might need some modification there. >> Nick n.j.cox@durham.ac.uk >> Sergiy Radyakin >> >> how do I get the list of variables used in an if-condition passed to >> my Stata program? >> obviously all sorts of logical expressions and functions are permitted >> in the if-condition. >> >> >> program foobar >> syntax [if] >> >> // ... determine which vars are used in the if-condition and put >> them in var_list ... >> // ... compute something ... >> >> end >> >> >> I am looking for an elegant solution, the one that would not involve, >> say, dropping vars one >> by one and checking if the expression is still computable. >> >> One solution is to replace all the ! ~ ^ + - * / = < > ] and ) to >> spaces, then look at the tokens left. >> Those with ( immediately following are function names, those with [ or >> a space immidetely >> following are variables. (and we can use -capture confirm variable- to >> check that). >> >> Is there any problem with such an approach? (e.g. factor variables in >> Stata 11?) >> Is there a better (or a standard/existing) approach to the problem? * * 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/

**References**:**st: Obtain the list of variables used in an if condition***From:*Sergiy Radyakin <serjradyakin@gmail.com>

**st: RE: Obtain the list of variables used in an if condition***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**Re: st: RE: Obtain the list of variables used in an if condition***From:*Jeph Herrin <junk@spandrel.net>

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