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From: John Darrington
Date: Tue, 3 Jul 2007 09:28:43 +0800
User-agent: Mutt/1.5.13 (2006-08-11)

On Mon, Jul 02, 2007 at 07:41:01AM -0700, Ben Pfaff wrote:
     John Darrington <address@hidden> writes:
     > On Sat, Jun 30, 2007 at 07:55:27AM -0700, Ben Pfaff wrote:
     >      There are a few subtleties I think.  First, I don't think we save
     >      a copy of the dictionary that corresponds to the active file.
     >      We'd need to do so, and then restore it for CLEAR
     > Spss doesn't do this.  So neither should we (at least not by default).
     I think that SPSS does do this.  The SPSS 13, 14, and 15 manuals
     all have an identical example that shows a data file being read,
     some transformations being done on it, and then running CLEAR
     TRANSFORMATIONS.  The text then states that the variables created
     by the transformations no longer exist, because they were created
     by transformations that have been discarded.

You're right!  The manuals do have this example.  I tried running that
example on v15 and it does exactly what the manual says it won't do!!
It DOES NOT remove the INDEXQ variable! (see attached output file).
So I suppose the question for us is, do we follow the manual or our
observations ?

     >      Second, some transformations are not exposed to the user and
     >      should not be cleared.  The specific one I have in mind is the
     >      DESCRIPTIVES transformation that produces Z scores.  As far as
     >      the user is concerned that transformation doesn't exist so it
     >      shouldn't be cleared.
     > Is this really an issue?  These transformations only come into
     > existance after the command has been called, and are destroyed before
     > it terminates, so there's no possibility that CLEAR TRANSFORMATIONS
     > can affect this.
     The transformation that I'm talking about does persist after the
     command terminates.  Take a look at cmd_descriptives and where
     the call to setup_z_trns is located.

Hmm.  I can see that this might cause problems for the GUI anyway.
When the descriptives command returns, the values of the z-scores will
not have been populated.

I can see that for optimisation reasons it's desireable not to execute
this transformation when running from a script, but the GUI needs to
run it, when it redraws the data sheet.  Otherwise the user will get
confused.   So maybe these "hidden" transformations should be
specially marked as such (perhaps in a seperate transformation chain)?


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