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Re: st: Contract/Collapse Combination


From   "Justina Fischer" <JAVFischer@gmx.de>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Contract/Collapse Combination
Date   Tue, 22 May 2012 16:46:00 +0200

I might be missing the point - but I would recommend a 'summarize' command or one of its versions (summarize by groups, etc).
This gives you both 'population' shares (means) but also the number of obs.

Justina
-------- Original-Nachricht --------
> Datum: Tue, 22 May 2012 07:37:52 -0700
> Von: Lucas <lucaselastic@gmail.com>
> An: statalist@hsphsun2.harvard.edu
> CC: Sam Lucas <lucaselastic@gmail.com>
> Betreff: Re: st: Contract/Collapse Combination

> Not really.  I was using X# in the statistical convention sense, not
> indicating that those are the true variable names.  I have about 150
> variables in the dataset.  I need a 15-way crosstab.  The variables in
> the crosstab have informative names, none of which start/end the same.
> 
> I provided too much information in my original post, and it is
> distracting from the central question, which I now realize is this:
> 
> Is there a way to use the contract command and obtain frequencies for
> TWO variables rather than just ONE?  A corollary question would be, Is
> there a way to use the contract command and obtain the count of 1's on
> TWO separate dichotomous variables?
> 
> I realize this is maybe a question for stata, but I cannot imagine I
> am the only person to ever need such a feature--I'm an original
> thinker, *maybe*, but not THAT original.
> 
> Such a command would allow one to easily reduce large datasets for
> processing in all those models for binary data that allow a frequency
> weight and/or a binomial option.
> 
> If someone has had this problem of needing two counts from the
> contract command and solved it, I'd love to know what you did.  And,
> if Dr. stata, whomever s/he is, has insight on the likelihood of this
> feature being added to contract, I'd love to hear it.
> 
> Thanks a bunch.
> Sam
> 
> On Mon, May 21, 2012 at 3:51 PM, Nick Cox <njcoxstata@gmail.com> wrote:
> > This sounds to me like
> >
> > contract x* entercol
> >
> > Nick
> >
> > On Mon, May 21, 2012 at 9:45 PM, Lucas <lucaselastic@gmail.com> wrote:
> >> So, I am attempting to construct a file containing a list-format 15
> >> (or so) -way crosstab, with frequencies of cases for each combination
> >> of values.  I have millions of cases, so this crosstab is appropriate.
> >>
> >> What would be ideal would be the ability to use the contract command
> >> but, instead of only indicating the need for one count,  could ask for
> >> the sum of two variables.  Assume I have a dichotomous variable (say,
> >> "enter college).  Those who enter college are coded 1, those who do
> >> not are coded zero.  I could then construct a new variable, named
> >> "DidNotEnter", coded 1 for those who do NOT enter college, and zero
> >> for those who do.
> >>
> >> If I could then write something like:
> >>
> >> collapse x1 x2 x3 x4 ... xj, freq(EnterCol) freq(DidNotEnter)  zero
> >>
> >> I could get the totals needed.  The plan is to speed processing of a
> >> computationally difficult model by substituting a model of counts for a
> >> model of individual cases.  To do this I need the total count of each
> >> combination and the count meeting the condition (e.g., entering
> college).
> >> My code above would, if possible, produce a file that allowed me to
> >> add the two frequencies to get the total.
> >>
> >> As far as I can tell, this is not possible.  What seems to be required
> >> is to run it with only the "Enter College" freq, then somehow break
> >> the two cases (EnterCollege=1 vs. EnterCollege=0) (or, alternatively,
> >> to keep EC==1 and run it, and then re-run with EC==0) and somehow
> >> combine them, an operation that seems to be begging for error in
> >> matching.
> >
> > *
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-- 
Justina AV Fischer, PhD
COFIT Fellow
World Trade Institute
University of Bern

homepage: http://www.justinaavfischer.de/
e-mail: javfischer@gmx.de. justina.fischer@wti.org
papers: http://ideas.repec.org/e/pfi55.html


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