Re: var_create_internal again

[john]

I'm of the opinion that var_create_internal should be dropped.

If you want to add an "internal variable", I think the best way
is to iterate the cases, and write them to a new casereader which 
has the extra variable.  A casereader-translator may make this easier.
Currently, we have a function called casereader_create_append_numeric - 
There is no corresponding casreader_create_append_string, but I suppose
one can be added if necessary.

Then, one can access the "internal" data with code like

const double x = case_data_idx (c, INDEX_OF_INTERNAL_DATA)->f;

or for alpha variables:

const char *s = value_str (case_data_idx (c, INDEX_OF_INTERNAL_DATA),
                           WIDTH_OF_INTERNAL_DATA);

The upper case symbols are just const int, or even simple macros.

I've been doing something similar this  week, and I've found that Ben's
new caseproto structure makes managing casereaders and their corresponding
cases a whole lot easier.

Hope this helps.

J'


On Fri, Jun 12, 2009 at 06:24:15PM -0400, Jason Stover wrote:
     I need to be able to set an interaction_variable's internal
     variable type to alpha.
     
     I need to do this in get_sum, in covariance-matrix.c. The problem
     is that the code needs to use some of the features in category.c,
     and that is hard to access without being able to see when an internal
     variable's type is alpha.
     
     Here is the purpose: The internal "interaction variable" is a variable
     essential to computations in GLM, but it's particular values won't be
     useful to the user. Right now, it can only be type numeric, which is
     causing the trouble.
     
     On IRC, Ben mentioned clarifying what var_create_internal is for, and
     either changing it, or dropping it, or using something else. So:
     What's the best way to make an "internal" variable, one whose values
     are to be hidden from the user, but that is used for computations?
     
     Here is a quick fix:
     
     struct variable *
     var_create_internal (int case_idx, int width)
     {
       struct variable *v = var_create ("$internal", width);
     ...
     
     This small change will allow an internal variable to be type alpha,
     which is OK by me.  But does it fit the idea of an "internal variable"
     in other uses?
     
     -Jason
     
     
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