st: -generate- and run time contingencies

[Mike Lacy <Michael.Lacy@colostate.edu>]

One feature of Stata with which I continue to experience difficulty 
concerns how to assign a value to a variable based on a run time 
contingency. As a simple illustration, consider the goal of assigning 
a uniform r.v. value to a variable, while rejecting values less than, 
say, 0.8.  If  -while- was sensitive to run time values of variables, 
I would do:

gen x = uniform()
while (x < 0.8) {
  replace x = uniform()
}

Obviously, this construct that would work in many languages does not 
work as desired in Stata, and just as obviously, there are other ways 
to accomplish the same end in Stata [  gen x = 0.8 + 0.2*uniform() ].


My question, then, concerns a general approach to these run-time 
contingencies, not all of which suggest simple workarounds to me. 
What seems most straightforward but clumsy as a generic approach is 
to do the code fragment involving the contingency as a matrix 
operation, and then save it back to a variable, e.g.,

matrix X = J(_N, 1, .)
local top = rowsof(X)
forvalues i = 1/`top'{
   scalar temp = uniform()
   while temp < 0.8 {
      scalar temp = uniform()
   }
     matrix X[`i',1] = temp
}
svmat X, name(MyVarName)


Any generic suggestions here?

Regards,



=-=-=-=-=-=-=-=-=-=-=-=-=
Mike Lacy
Fort Collins CO USA
(970) 491-6721 office






*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/