Re: st: -stylerules- updated on SSC

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

At 04:07 PM 4/13/2005 +0100, Nick Cox wrote:
> The package -stylerules- on SSC has been
> updated. I started by making a few changes
> in the light of Stata 9, but mostly thought
> of some other things to mention while
> I was doing that.
Some very good rules there Nick.  I'd be curious what thoughts people have 
about this one:

"Avoid preserve if possible. preserve is attractive to the programmer but 
can be expensive in time for the user with large data files.  Programmers 
should learn to master marksample."

Suppose I ignore that advise and instead do something like

preserve
keep if `touse'

1.  Will I gain some speed, because Stata will be working with a smaller 
data set and won't have to repeatedly process -if `touse'- commands?

2.  Isn't there a potential tradeoff between this and another rule, respect 
the dataset?  If you don't preserve, there is a greater burden on the 
programmer to make sure all is well at the end of the run.  But, isn't 
there also a greater risk if, say, the user stops the program before 
completion?

I suppose good, careful programmers can guarantee both speed and security 
of data.  But, I would add the caveat that, if you are not 100% confident 
of your programming, you might want to favor safety over speed.


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