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Tue, 17 Apr 2007 08:28:18 +0800
On Mon, Apr 16, 2007 at 01:53:54PM -0400, Jason Stover wrote:
On Mon, Apr 16, 2007 at 11:10:43AM +0800, John Darrington wrote:
> If we were to follow approach 2, am I right in thinking that the
> 'interaction' data structure could be as large as the number of
> cases in the casefile?
No. It would have either a hash of possible values (all unique), or a
small function to get back and forth between a union value and a
So, given an interaction involving N variables, from a datafile with M
observations, what is the upper bound on the size of this hash ?
> On the other hand, approach 1 sounds attractive, but there are things
> that need to be considered:
> a) They'd have to be a special class of variable, which would not
> normally be displayed, written to system files etc. So a new
> enum dict_class entry in variable.h would be required.
> b) I'm not sure how existing code would deal with these
> 'invisible' variables. For example many procedures might iterate
> through all the variables. So dict_get_var_cnt might have to
> take a parameter so that we'd know if we were interested in
> 'interaction' variables or not.
These statements make me think approach 2 is the way, especially
your comment b) above.
That's my feeling too, but I'm not familiar enough with the details to
What does Ben think?
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