Re: st: Re: Nearstat version

[Nick Cox <njcoxstata@gmail.com>]

In general I support programmers' rights (my program, my decision) but  
I have to say that this sounds distinctly eccentric. So in a database  
of Stata users if several people at StataCorp have the same  
coordinates the distance between them is the distance to the nearest  
Stata user, say several miles (km) away? To me it's zero. (Whether  
some purposes compel me to change zero to  some positive tolerance is  
a different issue.)
I'd recommend to Wilner

1. Documenting this quirk in the help if that's not done already. I  
guess most users of geographical data would regard it as a misfeature,  
to be frank.
2. Even if this default is what you want consider adding an option to  
override it.
3. In fact two options: zero means that; zero means a user-specfied  
tolerance.
Nick

On 6 Feb 2012, at 16:33, "P. Wilner Jeanty" <pwjeanty@gmail.com> wrote:

> 2012/2/5 Rüdiger Vollmeier <ruediger.vollmeier@googlemail.com>:
> > Thanks a lot for the good advice how to run the program.
> >
> > I ve got one question regarding the programming: It seems that in  
> > case
> > of non-identical observations with identical longitude and latitude,
> > the programs does not return the distance 0 but calculates the
> > shortest distance to non-identical latitude and longitudes. Am I
> > right? This is surprising and, I guess, for many users not desired.  
> > Is
> > it possible to change that (such that the distance 0 will be returned
> > in these cases)?
>
> This is a legitimate behavior by the program. Because it does not
> stand to reason that two different locations have identical latitudes
> and longitudes, -nearstat- thinks that it is computing the distance
> between an observation and itself. In order to identify the nearest
> neighbors (1st, 2nd, 3rd, and so forth), distance computed from an
> observation to itself is intentionally set to missing as part of the
> programming process. Ruediger's case where non-identical observations
> have identical latitudes and longitudes is an unusual one. As a
> result, I don't intend to modify -nearstat- to allow for it, at least
> not now, unless many users want this change to be made. Without more
> information, I find it odd that non-identical observations or areal
> units have identical latitudes and longitudes.
>
> FYI, a new version of -nearstat- with Mata code compiled in Stata 10.1
> has been submitted to SSC.
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