Matching minimum difference by group

[nbs98495]

Hello,

I have two datasets that look like the following:

Dataset 1:

sbdv	num	loc
150	0.876	1
160	0.993	1
171	0.937	1

Dataset 2:

sbdv	num	loc
120	0.987	0
121	0.965	0
123	0.945	0
125	0.912	0

I want to create a new dataset that contains all of dataset 1 plus a match of observations in dataset 2 of the observations with the minimum difference in 'num' between each obs in dataset 1 and all the obs in dataset 2.

So for sbdv = 150, I want to calculate the difference between its 'num' (0.876) and sbdv 120, 121, 123, and 125's respective 'num' values (0.987, 0.965, 0.945, 0.912). Then I want to save each 'match' to a new dataset containing all of dataset 1 and the matches for each observation.

So for this example, the new dataset would be:

sbdv	num	loc
150	0.876	1
160	0.993	1
171	0.937	1
125	0.912	0
120	0.987	0
123	0.945	0

I am guessing there is a straight forward solution, but I haven't been able to find anything that explicitly will do this.

[PGStats]

You don't need to know which observation from ds 2 match each observation from ds 1?

[nbs98495]

No, just match ds 1 obs to ds 2 based on ds1 num - ds2 num

[PGStats]

When you say "minimum difference" do you mean absolute value of difference?

[nbs98495]

Yes!

[PGStats · Accepted solution]

Assuming the pairing has to be one-to-one, this can be expressed as a linear assignment problem and solved easily with PROC OPTNET (a proc of SAS/OR):

data ds1;
input sbdv  num loc;
datalines;
150   0.876   1
160   0.993   1
171   0.937   1
;
data ds2;
input sbdv  num loc;
datalines;
120   0.987   0
121   0.965   0
123   0.945   0
125   0.912   0
;

proc sql;
create table pairs as
select 
    ds1.sbdv as from,
    ds2.sbdv as to,
    abs(ds1.num-ds2.num) as weight
from ds1, ds2;
quit;

proc optnet data_links=pairs direction=directed;
linear_assignment out=selected_pairs;
run;

proc sql;
create table want as 
select sbdv, num, loc
from
    (select sbdv, num, loc from selected_pairs, ds1 where from=sbdv) 
    union all
    (select sbdv, num, loc from selected_pairs, ds2 where to=sbdv);
quit;

[nbs98495]

This works perfect, thanks!

[Ksharp]

data ds1;
input sbdv  num loc;
datalines;
150   0.876   1
160   0.993   1
171   0.937   1
;
data ds2;
input _sbdv  _num _loc;
datalines;
120   0.987   0
121   0.965   0
123   0.945   0
125   0.912   0
;
data want;
 if _n_=1 then do;
   if 0 then set ds2;
   declare hash h(dataset:'ds2');
   declare hiter hi('h');
   h.definekey('_sbdv');
   h.definedata(all:'y');
   h.definedone();
 end;
set ds1;
min=999999;
do while(hi.next()=0);
  dis=abs(num-_num);
  if dis<min then do;min=dis;sbdv1=_sbdv;num1=_num;loc1=_loc;end;
end;
h.remove(key:sbdv1);
drop _:  min dis;
run;