data yourdata;
    set yourdata;
    Position1=scan(Position,1,',');
    Position2=scan(Position,2,',');
    Position3=scan(Position,3,',');
run;

共同学习了

More details below.

I did not know scan function; it was very nice. If I don't know scan, this is what I would do:

data test;
input name $1. position $50.;
cards;
A P1,P2,P3
B P1
C P1,P2, P3, P4
D P1,P2, P3, P4, P5
E P2, P5
run;


data out(keep=name position position1-position5);
    length name $10. position $50.;
    length position1-position5 $10.;   
    array positions[5] $ Position1-Position5;
    set test;
    rest = position;
    do p=1 to 5;
            loc = index(rest, ",");
            if loc > 0 then do;
                    positions[p]=substr(rest, 1, loc-1);
                    rest = substr(rest, loc+1, length(rest));
            end;
            else do;
                    positions[p] = rest;
                     p = 6;
           end;
end;
run;

外部文件用infile语句，dlm选项(dlm="，")