Re: st: RE: programming problem

[Jeph Herrin <junk@spandrel.net>]

Never noticed -concat- before. Nice.

thanks,
Jeph

Nick Cox wrote:
> This problem is, in my view, an awkward little challenge. 
> I very nearly posted a solution that was _quite_ 
> wrong. 
> A -reshape- solution, as exemplified by Sebastian's code,
> looks awkward for just this problem, but may of course be a good
> idea for a variety of other problems. 
> A quite different idea runs like this: 
> egen history = concat(var1-var12) 
> gen byte mycond = substr(history, month, 1) == "1" 
> The appearance here of avoiding a loop over variables
> is illusory, as a  loop is hidden inside -concat()- 
> (and even as of Stata 10 it is still a -while- loop). 
> But a concatenated history makes some other problems 
> easy, even with this wide data structure. 
> Has this person experienced a spell of three or more months 
> with this condition?  
> gen byte spell3 = strpos(history, "111") > 0 
> When was the first month in the year with 
> this condition?  
> gen byte first = strpos(history, "1") 
> When was the last month in the year with 
> this condition? 
> gen byte first = cond(first, 13 - strpos(reverse(history), "1"), 0)  
> Nick 
> n.j.cox@durham.ac.uk 
> Jeph Herrin
>  
> > Duh.
> >
> > I had done this:
> >
> >   forval j = 1/12 {
> >    	replace mycond =  `j' == month & var`j' == 1
> >   }
> >
> > Which effectively only tests month 12, before I veered
> > off in another direction.
>  
> Nick Cox
>
>
> > > Short of a solution using -reshape-, I think
> > > this will suit: 
> > > gen mycond = 0 
> > > forval j = 1/12 { 
> > > 	replace mycond = 1 if `j' == month & var`j' == 1 
> > > } 
> > > where I assume that your -var*- are 1 when true. 
>  
> Jeph Herrin
>  
> > > > I have observations on patient admissions over
> > > > a 12 month period.
> > > >
> > > > For each observation, I have 12 variables, call
> > > > them var1-var12, which indicate whether a certain
> > > > condition was met for that patient for months 1-12.
> > > > So, eg, it may be true for months 1-3 and 7-12.
> > > >
> > > > I also have a variable -month-, which indicates
> > > > the current month of the observed admission. What
> > > > I want to capture is whether the condition was true
> > > > in the month of admission.
> > > >
> > > > For instance, at first I unthinkingly tried this:
> > > >
> > > >   gen mycond = var`=month'==1
> > > >
> > > > but this of course uses the first observed value
> > > > of -month-, which happens to be 6, and only checks
> > > > -var6-.
> > > >
> > > > I eventually got there by creating lots of vars, but is
> > > > there a more direct solution?
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