Nearest neighbour in SAS - sas

Question

I have a point data set containing latitude, longitude and elevation data. I would like to identify the nearest neighbour of a given point by using the distance between any two given points (2d or 3d). Could anybody suggest the different methods available in SAS for such geo-spatial data analysis and an example SAS code? Thanks.

Answer 1

Your best bet is to look into the clustering procedures, as KNN style clustering is pretty close to what you want (and at minimum cluster analysis can get you to a 'set' of neighbors to check). PROC MODECLUS, PROC FASTCLUS, PROC CLUSTER all give you some value here, as does PROC DISTANCE which is used as input in some cases to the above. Exactly what you want to use depends on what you need and your speed/size constraints (PROC CLUSTER is very slow with large datasets, but gives more useful results oftentimes).

Answer 2

Here is an example of nearest-neighbour calculation via the use of SQL (given in the SAS help file somewhere):
options ls=80 ps=60 nodate pageno=1 ;
data stores;
input Store $ x y;
datalines;
store1 5 1
store2 5 3
store3 3 5
store4 7 5
;
data houses;
input House $ x y;
datalines;
house1 1 1
house2 3 3
house3 2 3
house4 7 7
;
options nodate pageno=1 linesize=80 pagesize=60;
proc sql;
title 'Each House and the Closest Store';
select house, store label='Closest Store',
sqrt((abs(s.x-h.x)**2)+(abs(h.y-s.y)**2)) as dist
label='Distance' format=4.2
from stores s, houses h
group by house
having dist=min(dist);
quit;

Answer 3

I wrote 2 macros to accomplish this!
first macro to take one input gps location and use the lat and lon as a set value new variables for the "neighbor" location dataset. compute all distance and select the min value and store in temp dataset.
second calling macro loop through the input datset and to pass in the indivial gps location, call the first macro to do the work and append each min distance to my output dataset.
/*** first concatenate your input lat, lon as well as some id into a | seperate long string for later %scan into individual input ***/
%macro min_distance;
data compute_all_dis;
set all_neighbor_gps_locations;
/** here create a new variable to this big dataset with the one point gps value***/
first_lat = &latitude;
first_lon = &longitude;
ID = .
/** compute all **/
distance = geodist(lat, long, first_lat, first_lon, 'dm');
run;
/** get the shorted distance***/
proc sql;
create table closest_neighbor as
select milepost,OFF_PERIOD_ID, lat, long, first_lat, first_lon, distance
from compute_all_dis
having distance = min ( distance);
quit;
%mend min_distance;
%macro find_all_closest_neighbors;
data _null_;
runno=countw("&ID",'|');
call symputx('runno',put(runno,8.));
run;
%put &runno;
%do i=1 %to &runno;
%let PERIOD = %SCAN(&OFF_ID, &i, "|");
%let latitude = %SCAN (&LAT_I, &i, "|");
%let longitude = %SCAN (&LONG_I, &i, "|");
%min_distance;
proc datasets nowarn;
append base= pout.all_close_neighbors data=closest_neighbor;
run;
%end;
%mend find_all_closest_neighbors;
%find_all_closest_neighbors;