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st: RE: RE: dangerous preserve


From   "Martin Weiss" <martin.weiss@uni-tuebingen.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: dangerous preserve
Date   Sun, 20 Apr 2008 17:55:15 +0200

Nick,

fair enough, but it should be possible to advise just the way Stata advises
if the change flag for the dataset is 1. Fortunately, it gives a warning as
to the changed nature of the data you are about to destroy and prevents you
from doing stupid things. I remember reading a section in the handbooks
about how Stata is so very careful with commands that may change your data
in undesirable ways. Should the same not happen for -preserve-d data?

Martin Weiss
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-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
Sent: Sunday, April 20, 2008 5:46 PM
To: statalist@hsphsun2.harvard.edu
Subject: st: RE: dangerous preserve

I think this is mostly on the level of yes, sharp knives can cut you if
you are not careful. 

As I understand it, 

preserve
...
save 
...

does not rule out a subsequent -restore-. 

But otherwise yes, you can get bitten if you forget what you have done. 

It would be easy enough to write a command that -save-d while it
-preserve-d, but 
you would have to remember to use it. I can't see an advantage in
advising that 
over advising the use of -save- before -preserve- when that's a good
idea -- or indeed over recommending -save- and avoiding -preserve- if
you are going to forget what you have done. 

Nick
n.j.cox@durham.ac.uk 

Martin Weiss

I was wondering if anyone apart from me has been bitten by -preserve-? I
recently preserved data, then dropped half my data to carry out some
calculations and later forgot the preserve-status and saved. Now call me
foolish, but in the heat of the action, it is easy to forget about the
status of your data, isn`t it?
So: is there a mechanism to alert me to this danger, and if not, should
there be one?

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