Primary Key using SAS

Question

I would like a SAS program to find the primary service from a data set based on the line with the highest rate but when there is a tie make the first line primary. See data set below.

ID   line rate  outcome
TTT   1    .95  Primary
TTT   2    .43
RRR   1    .75  Primary
RRR   2    .75
AAA   1    .23
AAA   2    .12
AAA   3    .65  Primary

I created two tables with the same data, then used the following

Code used:

proc sql;
  create table test as
  select a.ID, a.line, a.rate
    (case 
       when ((a.ID = b.ID) and (a.rate ge b.rate)) then "Primary" 
       else ' ' 
    end) as outcome
  from table1 a,table2 b
  where a.ID = b.ID;
quit;

Answer 1

This probably isn't the best solution but I recommend a two step process.

1. Find the max for each ID
2. Assign Primary key. Use a flag variable to indicate if the max_rate is the first occurrence.

Here's an untested sample code:

    *Calculate max rate per ID;
    proc sql;
    create table temp1 as
    select a.*, max(rate) as max_rate
    from table1
    group by ID
    order by ID, line;
    quit;

    *Assign primary key;
    data want;
    set temp1;

    by ID;
    retain flag 0;

    if first.ID then flag=0;
    if rate=max_rate and flag=0 then do;
       flag=1;
       key='Primary';
     end;
     run;

    proc print data=want;
    run; 

Another option is a data step with sort, sort so you have the maximum with the minimum line at the top and use BY processing to set the key to Primary.

 proc sort data=have;
 by ID descending rate line;
 run;

 data want;
 set have;
 by id;
 if first.id then key='Primary';
 run;

 proc sort data=want;
 by id line;
 run;

proc print data=want;
run;