Re: st: RE: Taking averages, etc.

[Richard Williams <Richard.A.Williams.5@nd.edu>]

At 12:38 PM 12/17/2003 +0000, Allan Reese wrote:
> First point is to analyse the logic.  Reforming a problem often speeds up
> the execution far more than fancy coding, and leads to insights.  In this
> case:
>   gen y=5
>   replace y=3 if x1==1 & x2==3
>   replace y=4 if y==5 & (x3==2 & x4==17)
>
> performs far fewer tests.  The parentheses do not affect the result but
> emphasise the logic.
I'm not sure how that performs fewer tests.  The if-then-else structure 
only performs as many tests as are necessary whereas the above would 
perform 2 tests for each case.  In any event, I think I'd be more likely to 
make errors with syntax like this.  But that may just be me!


> Stata, as Nick has already replied, has a completely general control
> language that includes if/then/else, for and while.  Unlike SPSS, where
> only data transformations can be put into DO IF and LOOP constructions,
> Stata allows any statements or blocks of statements.  These may
> conveniently be written using an editor (provided it doesn't add a file
> extension!) and saved as .DO or .ADO on the fly.
You must get Nick's messages faster in the UK!  I look forward to what he 
has to say.  Thanks Allan.


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