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Re: casefile random access
From: |
Ben Pfaff |
Subject: |
Re: casefile random access |
Date: |
Wed, 07 Jun 2006 21:45:23 -0700 |
User-agent: |
Gnus/5.110004 (No Gnus v0.4) Emacs/21.4 (gnu/linux) |
John Darrington <address@hidden> writes:
> Great. The only problem is, that the comment at the top of the file
> which says that casereaders cannot randomly seek, is no longer true.
Fixed now.
> I had a look at the GUI again last night. A number of problems are
> beginning to come apparent. One is the issue of inserting/deleting
> cases in the middle of a casefile; I don't think it's possible. I'm
> thinking of having some kind of auxiliary structure to store
> inserted/deleted cases. Or perhaps casefiles can be extended to allow
> us to do that?
>
> Another issue, is that casefiles have a fixed value_cnt, which makes
> inserting/deleting variables difficult. I think the way around this
> problem is to run a procedure whenever the dictionary is changed.
It is possible, but nontrivial, to fix casefiles to solve both of
these problems.
Cases could be inserted by adding a second file and reading its
data partway through the middle of the first one; some kind of
index would be necessary. Deleting cases is simpler; you just
arrange to ignore the ones that are deleted. If this sort of
thing is taken to its logical extreme, you end up with a database
system like Berkeley DB's Recno access method.
Variables could be inserted by adding a second file and reading
it in parallel with the first one. To delete a variable, ignore
that data as you read it.
How important is it to solve these problems at the casefile
level?
--
Ben Pfaff
email: address@hidden
web: http://benpfaff.org
- casefile random access (was: Re: PSPP conference call notes.), (continued)
- casefile random access (was: Re: PSPP conference call notes.), Ben Pfaff, 2006/06/03
- Re: casefile random access, John Darrington, 2006/06/03
- Re: casefile random access, Ben Pfaff, 2006/06/05
- Re: casefile random access, John Darrington, 2006/06/05
- Re: casefile random access, Ben Pfaff, 2006/06/05
- Re: casefile random access, John Darrington, 2006/06/06
- Re: casefile random access, Ben Pfaff, 2006/06/06
- Re: casefile random access, John Darrington, 2006/06/06
- Re: casefile random access, Ben Pfaff, 2006/06/06
- Re: casefile random access, John Darrington, 2006/06/07
- Re: casefile random access,
Ben Pfaff <=
- Re: casefile random access, John Darrington, 2006/06/08
- Re: casefile random access, John Darrington, 2006/06/08
- Re: casefile random access, Ben Pfaff, 2006/06/08
- Re: casefile random access, John Darrington, 2006/06/08
- Re: casefile random access, Ben Pfaff, 2006/06/08
- Re: casefile random access, John Darrington, 2006/06/12
- Flexifiles, John Darrington, 2006/06/24
- Re: Flexifiles, Ben Pfaff, 2006/06/24
- Re: Flexifiles, John Darrington, 2006/06/25
- Re: Flexifiles, John Darrington, 2006/06/28