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Re: st: Calculating Euclidean Distance


From   Austin Nichols <austinnichols@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Calculating Euclidean Distance
Date   Thu, 10 Jun 2010 09:59:13 -0400

Anthony Laverty <anthonylav@googlemail.com> :
If you have N hospitals at T points in time, then you will have NTxN
squared distances in your variables, and if they are doubles you may
well run out of memory long before that, but if all you want is the
nearest hospital, then you want one variable per hospital giving the
identity of the nearest (over all months, you seem to suggest). You
might also want to compute distance on a log scale, or some other
metric. With more detail on your problem, you may get a better answer.
Nevertheless, this is like what you asked for, I think:

clear
input str1 hospital time patients
 A 1 456
 A 2 759
 A 3 236
 B 1 214
 B 2 854
 B 3 325
 C 1 250
 C 2 321
 C 3 852
end
egen g=group(hospital)
su g, mean
loc N=r(max)
forv i=1/`N' {
 g double d`i'=.
}
levelsof time, loc(ts)
fillin time g
sort time g
g long obs=_n
qui foreach t of loc ts {
 su obs if time==`t', mean
 loc n0=r(min)
 loc n1=r(max)
 forv i=`n0'/`n1' {
loc n=`i'-`n0'+1
replace d`n'=(patients-patients[`i'])^2 if inrange(_n,`n0',`n1')
 }
}
l, sepby(time) noo

On Thu, Jun 10, 2010 at 5:08 AM, Anthony Laverty
<anthonylav@googlemail.com> wrote:
> Dear Statalist
>
>
>
> I have data on patient numbers at various hospitals and am trying to
> calculate a new variable which is the Euclidean distance between one
> specific hospital (say A) and all of the others, so that i can select
> which hospitals had the most similar number of patients across all
> months.  The data is more or less arranged like this (although it has
> a few more columns not of direct interest to this question):
>
> Hospital     Time           Patients
> A                 1                 456
> A                 2                 759
> A                 3                  236
> B                 1                 214
> B                 2                 854
> B                 3                 325
> C                 1                 250
> C                  2                321
> C                  3                852
>
>
>
> So, i want to cycle through each time period and calculate the
> difference squared between hospital A and all of the other hospitals
> individually as one new variable.
>
>
>
> Any suggestions greatly appreciated
>
>
>
> Anthony Laverty

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