st: Re: if then else

[Christopher F Baum <baum@bc.edu>]

On Dec 18, 2003, at 2:33 AM, Richard wrote:

> > And for an obtuse solution:
> >
> >
> > . g c1=3*(x1==1 & x2==3)
> >
> > . g c2=4*(x3==2 & x4==17)
> >
> > . g y= cond(max(c1,c2),max(c1,c2),5)
> >
> > . list x1-x4 y
> >
> >      +-----------------------+
> >      | x1   x2   x3   x4   y |
> >      |-----------------------|
> >   1. |  1    3    0    0   3 |
> >   2. |  0    0    2   17   4 |
> >   3. |  1    2    3    4   5 |
> >   4. |  1    3    2   17   4 |
> >   5. |  1    2    3    4   5 |
> >      +-----------------------+
> No, something is wrong there; on case 4, my SPSS code would result in 
> y =
> 3, not y = 4 like you have it.
Richard has indicated that SPSS "short-circuits" on an IF/THEN/ELSE, 
breaking out of the construct whenever one of the conditions is 
satisfied. Some programming languages do that, and some do not. All the 
more reason to have some very explicit logic (that does not depend on 
the rules that a specific piece of software follows). My solution was a 
literal translation of his evaluating several conditions in turn, but 
without the understanding of how his software will deal with multiple 
satisfied conditions. If code is to be portable and readable, that 
understanding becomes part of the documented scheme.

Of course many unfamiliar with Stata have argued that its language is 
not partiicularly readable, at least at first glance: a recent Swedish 
visitor said "what's with all of those backticks"? I told him the funny 
story of my terminal emulator which  remapped backtick to tick, and 
hours of frustration trying to change a few lines of code in Unix 
Stata.

Kit

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