st: selecting subsets of data based on date with which to calculate geonear (SSC)

["Ben Hoen" <bhoen@lbl.gov>]

Happy Holidays!

I am trying to find a way to loop through cases in a file, while selecting a
subset of that file (based on date) with which I would execute a
geonear(SSC) calculation with them. Specifically, for each case in the file,
I would like to select the nearest 5 neighbors that have a date which is
equal to or within the preceding 6 months.

I have some comfort with how to execute the geonear(SSC) part of it, but
seem to be lost with how to select subsets of data based on a particular
case.  

Here is my (feable) attempt to build this code.  I (clearly) nonplussed how
to do what I hope to do, but figure there are many examples.  If you have
any advice, links, etc, I would be greatly appreciative.

Best wishes for the holidays.  

Best,

Ben

=====================
set seed 1234
sysuse auto, clear
gen ylat = 41+runiform()  //to create a latitude
gen xlong = -73-1*runiform() //to create a longitude
gen date=16500+(int(500*runiform())) //to create dates that a within a few
years of each other
format date %tdnn/dd/YY
g id=_n //to create an id
keep id ylat xlong date price
order id price date ylat xlong

tempfile all nnset tempest  //to create temp files to be used in the loop
below
save "`all'" //saving the full dataset
clear
g emptyvar=. //to create a empty variable so I can save an empty dataset
save "`tempset'" // saving off the empty dataset

local N=_N //to establish the number of cases

forvalues i = 1/N { //I am trying here to begin a loop through the cases
	local maxdate=date
	local mindate=date-180
	keep if date>=`mindate' & date <=`maxdate' // my attempt to select a
group of cases
	save "`nnset'" // and to save off that group
	geonear id ylat xlong using `nnset', n(id xlong ylat) ignore
nearcount(5) miles //store info about the 5 nearest neighbors from the
subset
	append using "`tempset'" //append the case to the temp file
	}
*
===============================================



Ben Hoen
Principal Research Associate
Lawrence Berkeley National Laboratory
Office: 845-758-1896
Cell: 718-812-7589
bhoen@lbl.gov
http://emp.lbl.gov/staff/ben-hoen

Visit our publications at: 
http://emp.lbl.gov/publications




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