Hello,
I’m searching a proc in sas to find the K nearest neighbors in a set of points.
In the following data step, I generate a random set of 100 observations.
DATA observations;
do ID=1 TO 100;
x1 = RAND('NORMAL',0,1);
x2 = RAND('NORMAL',0,1);
x3 = RAND('NORMAL',0,1);
output;
end;
run;
For example, with this set of 100 observations, is there a proc to search the 10 nearest neighbor (Euclidian distance) of the point [ 0.5 ; 0.5 ; 0.5 ]?
Please note that I already found proc discrim to apply a KNN classification. But I want the list of the K nearest neighbor and not to make a classification.
Thx!
Why not just code it yourself?
data observations;
do ID=1 TO 100;
x1 = RAND('NORMAL',0,1);
x2 = RAND('NORMAL',0,1);
x3 = RAND('NORMAL',0,1);
output;
end;
run;
proc sql noprint ;
create table distance as
select distinct id,x1,x2,x3,sqrt((x1-y1)**2 + (x2-y2)**2 + (x3-y3)**2) as distance
from observations
, (select 0.5 as y1,0.5 as y2, 0.5 as y3 from observations(obs=1) )
order by distance desc
;
quit;
data top10;
set distance (obs=10);
run;
proc print; run;
One quick way to find nearest neighbors in a large set of observations is PROC MODECLUS. Your specific problem could be solved by:
DATA observations;
do ID=1 TO 100;
x1 = RAND('NORMAL',0,1);
x2 = RAND('NORMAL',0,1);
x3 = RAND('NORMAL',0,1);
output;
end;
run;DATA position;
ID = -999;
x1 = 0.5;
x2 = 0.5;
x3 = 0.5;
run;proc sql;
create table test as
(select * from position)
union all
(select * from observations)
order by ID;ods _all_ close;
proc modeclus data=test dk=11 /* = 10 observations + 1 position */ neighbor;
var x1 x2 x3;
id ID;
ods output Neighbor=nTest;
run;ods listing;
proc sql inobs=10;
select nBor as ID, distance from nTest;
Hello Tom & PGStats,
many thanks for your help !
based on the message from Tom, I have buil the following macro "listOfKNN":
data observations;
do ID=1 TO 100000;
x1 = RAND('NORMAL',0,1);
x2 = RAND('NORMAL',0,1);
x3 = RAND('NORMAL',0,1);
output;
end;
run;
%macro listOfKNN (obser , target, K, nameOutput);
%Let dim = %eval(%SYSFUNC(count(&target,%NRSTR( )))+1) ;
%let ttt =;
%DO ii = 1 %TO &dim;
%let ttt = &ttt.(x&ii.-%scan(&target,&ii," "))**2;
%IF &ii NE &dim %THEN
%let ttt = &ttt.+;
%END;
proc sql noprint ;
create table &nameOutput as
select distinct *, sqrt(&ttt)as distance
from &obser
order by distance;
quit;
data &nameOutput;
set &nameOutput (obs=&K);
drop distance;
run;
%mend listOfKNN;
/*make a test*/
%listOfKNN( obser = observations,
target = 0.5 1 1,
K = 5,
nameOutput = out
);
B.R.
Olivier
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