OK, last trial. Change of tool, but still seeking something more efficient than brute force (computing over 5e8 geodetic distances).
Seeking maximum case number inside a 0.5 mile radius circle, centered on a case :
/* Transform Long and Lat into cartesian coordinates centered
roughly on the median location. Use yr_state_case as a unique case No. */
%let latRef=36;
%let lonRef=-87;
proc sql;
create table cases as
select yr, state, 'case'n, latitude, longitud,
catx("_",yr,state,'case'n) as caseNo length=12,
geodist(latitude,longitud,&latref,longitud,"M")*sign(latitude-(&latref)) as Y_Mi,
geodist(latitude,longitud,latitude,&lonref,"M")*sign(longitud-(&lonref)) as X_Mi
from Table;
quit;
/* Guess a maximum value for the number of cases in a cluster, increase if needed */
ods _all_ close;
proc modeclus data=cases dk=50 neighbor;
var X_Mi Y_Mi;
id caseNo;
ods output Neighbor=nCases(where=(distance<=0.5));
run;
ods listing;
/* Fix missing values in ODS table */
data ncases(drop=controlVar rID);
retain rID;
set ncases;
if missing(ID) then ID = rID;
else rID = ID;
run;
proc sql;
create table clusters as
select ID, count(*) as n from nCases group by ID;
/* Extract all big clusters */
create table bigClusterCases as
select ID, nbor, distance, count(*) as n, max(distance) as maxDist
from nCases
group by ID
having count(*) >= (select max(n)-9 from clusters)
order by n descending, maxDist, ID;
/* Find significantly overlapping clusters, inside each pair, indicate the
biggest and the best centered */
create table centerPairs as
select a.ID, a.nbor
from bigClusterCases as a inner join bigClusterCases as b
on a.nbor=b.ID and b.nbor=a.ID and (a.n>b.n or (a.n=b.n and a.maxDist<b.maxDist));
/* Drop the smaller or not as well centered overlapping clusters */
delete from bigClusterCases
where ID in (select nbor from centerPairs);
select unique
n label="Nb Cases in Cluster",
ID label="Cluster Center (Yr_State_Case)",
maxDist label="Maximum Inter-case Distance (mi)"
from bigClusterCases
order by n descending;
quit;
--------
Cluster Maximum
Nb Cases Center Inter-case
in (Yr_State_ Distance
Cluster Case) (mi)
28 2008_36_305 0.468079
27 2005_36_139 0.4915
22 2004_36_1151 0.499706
PG
PG
