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Re: data sets and caching

From: Ben Pfaff
Subject: Re: data sets and caching
Date: Wed, 02 Nov 2005 07:42:00 -0800
User-agent: Gnus/5.110004 (No Gnus v0.4) Emacs/21.4 (gnu/linux)

Jason Stover <address@hidden> writes:

> First, I should draw a distinction between 'residuals' and 'models'
> here. Pardon me if I'm saying something everyone already knows.

No, thanks for pointing out the difference.  You probably told me
about residuals vs. models before, but I forgot.

> and there are as many residuals as cases.

So the residuals should be in the working file, then, as extra
variables?  They're not really part of the dictionary, they're
part of the data.  If I understand correctly, of course.

> The 'save' subcommand appends the residuals to the current working
> file, as a new variable. The residuals aren't really part of a
> 'statistical model', but some 'model caches' in PSPP should probably
> include residuals. And yes, the residuals should be included in the
> dictionary, to answer the question above.

Oh yes, it seems that I understand, then.


>> Should it be possible to save them to and retrieve them from
>> separate files?  (Maybe the SAVE/XSAVE command could support an
>> option that saves models without associated data.)
> I think this is a swell idea. Right now, SPSS' OUTFILE subcommand with
> the MODEL keyword saves the model information as XML. 

That seems like a reasonable approach too--is there a reason to
overload SAVE/XSAVE in that case?

> Given that PSPP should be able to save a model object, then load it
> later, perhaps with an entirely different, inappropriate data set, the
> model object should probably store some information from the
> dictionary in use at the time the model was created. In particular,
> that model object should know if a user asks it to do something
> impossible, such as using a string variable in a place where a numeric
> variable belongs.

Makes sense.
Ben Pfaff 
email: address@hidden

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