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RE: st: Getting the exact number of obs. a graph is based on


From   Jesper Kjr Hansen <jkh-stata@msecon.eu>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Getting the exact number of obs. a graph is based on
Date   Tue, 2 Oct 2007 06:43:19 +0200

Austin,

point taken. i.e., it's hard to determine the exact number of observations used in
more complicated graphs such as overlaid graphs. I'll make due with the current
ad-hoc solutions to determining the number of obs.

/Jesper

> 
> Jesper Kjr Hansen <jkh-stata@msecon.eu>:
> 
> I don't think there is one procedure that would work for all graphs.
> You might think a -serset- call would give that info, but many graphs
> do not encode information on all observations used (e.g. -gr box-
> throws out a lot of info).  A -tw- graph might use information on 100
> observations but use different observations for different plots on the
> same graph, so it's not clear what number(s) should be reported in
> every instance.  E.g. in
> 
> sysuse auto, clear
> replace pr=. if rep78==1
> replace wei=. if rep78==2
> scatter pr wei mpg
> 
> what number of obs would you like returned?  In any case, I think your
> general approach will work for most cases you might care about, but I
> would remind you to include weights as a qualifier (perhaps accounting
> for zero, negative, and missing weights as applicable) too.
> 
> On 10/1/07, Jesper Kjr Hansen <jkh-stata@msecon.eu> wrote:
> > I think I know the answer to this one, but just to be sure:
> >
> > Is there any formal procedure/option/returned result for 
> identifying the exact number
> > of observations a graph is based on, documented or 
> otherwise... besides first
> > principles using -count- -sum- and others, that is.
> >
> > For example:
> >
> > -count if !mi(<all vars used in graph>) & [if statement | in range]-
> >
> > The solution works well, but sometimes I can't help 
> thinking that the graph command
> > should return the number of observations used - just like 
> an estimation command.
> >
> > /Jesper
> 


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