proc sort data=aaa;
    by var2;
run;

data bbb;
    set aaa;
    by var2;
    retain y;
    if first.var2 then y=x;
run;

proc sort data=bbb out=ccc(drop=y);
    by descending y;
run;

data aaa;
input var1$ var2$ x;
cards;
aa aa 5
轻 aa 3
中 aa 2
重 aa 0
bb bb 8
轻 bb 5
中 bb 3
重 bb 0
cc cc 6
轻 cc 6
中 cc 0
重 cc 0
;
run;

下面的代码是不是满足要求？

data aaa;
input var1 $ var2 $ x;
cards;
ttl aa 5
l1 aa 3
l2 aa 2
l3 aa 0
ttl bb 8
l1 bb 5
l2 bb 3
l3 bb 0
ttl cc 6
l1 cc 6
l2 cc 0
l3 cc 0
;
run;

proc transpose data=aaa out=bbb;
  by var2;
        id var1;
        var x;
run;

proc sort data=bbb;
  by descending ttl;
run;

data ccc;
  set bbb;
        array level{4} ttl l1 l2 l3;
        do i=1 to 4;
    if ^missing(level{i}) then levelv=level{i};
                varname=vname(level{i});
                output;       
        end;  
        keep var2 varname levelv;
run;