st: RE: RE: RE: AW: Creating index relative to other observations

["Frederick Guy" <f.guy@bbk.ac.uk>]

Many thanks. Now for a crash-course in MATA...

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
Sent: 29 April 2010 19:22
To: statalist@hsphsun2.harvard.edu
Subject: st: RE: RE: AW: Creating index relative to other observations

I'd do this in Mata. Mata has a -for- loop. 

Nick 
n.j.cox@durham.ac.uk 

Frederick Guy

Thanks, I guess I was unclear on this aspect of the problem. For each
observation, the sum I'm talking about is of measurements made relative
to all other observations (or more generally, to some set of other
observations) in the sample.

Martin Weiss

".. sum up the results of these computations,".

Creating sums can mean different things in Stata. It may sound trite,
but
the easiest is simply to -generate- a sum by adding values with a "+"
sign.
If you want the total of a variable, look at -egen, total()-. If you
want a
running sum, take a look at -help sum()-.

Frederick Guy

I have need to use information from all observations (about 1800 of
them) to create a new variable.

The variable created is a weighted sum of the inverse of geographical
distances between observation i and all j n.e. i. I have longitude and
latitude for each observation, and computation of the distance from any
i to any j is straightforward. What I don't know is how to get Stata to
loop over all observation and sum up the results.

For every observation i, I think I need to

(a) loop through all j n.e. I, doing computations involving variables
x1, x2(i) and x1, x2(j), and then

(b) sum up the results of these computations, returning a value which
becomes variable x3 for that i.

I expect there's a straightforward way to do this. Any suggestions?

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