options ls=65 ps = 50 nocenter; run;

proc format ;
value codes 1="G" 2="E" 3="ND" 4="S";
run;

data a;   * 1=G  2=E 3=ND 4=S ;

array ic(4) G E ND S;

input c math1 math2;

do i =  1 to 4; ic(i)=(c=i); end;

math1c = math1 - 4.9821429; /* so mean of ND+S group is zero */ 

lines;
2  8  6
3  9  8
3  4  4
1  3  1
1  5  2
1  5  4
1  6  5
2  2  2
2  8  5
2  5  7
1  5  2
2  3  4
2  6  7
2  3  3
2  4  9
2  5  3
2  5  5
3  4  5
3  4  4
3  4  3
1  2  6
1  4  4
1  4  4
1  7  6
1  3  3
1  3  4
1  4  2
1  3  2
2  4  5
2  6  6
2  7  7
2  3  2
2  8  5
2  6  6
2  4  6
3  3  4
3  5  3
3  5  6
3  3  3
1  2  3
1  2  3
1 10  2
2  5  3
1  3  1
1  5  5
1  3  2
1  2  1
1  2  2
3  2  4
3  1  2
1  9  8
2  7  8
2  2  5
2  5  3
1  5  5
3  6 10
1  4  3
1  8  9
2  5  6
2  6  4
3  7  9
3  7  8
3  4  5
3  9  6
3  3  2
4  2  3
4  7  6
4  1  1
4  4  5
4  6  3
4  5  7
4  6  5
4  6  3
4  6  2
4  9  8
4  5  5
4  4  4
4  6  8
4  8  2
4  9  6
4  6  2
4  5  2
3  2  2
4  4  4
4  4  4
4  4  3
3  2  4
3  4  3
2  5  5
2  7  8
2  6  5
2  6  6
1  7  6
1  4  3
1  5  2
4  4  0
4  6  5
4 13  7
4  7  6
3  6 10
3  5  6
3  3  6
3  6  3
4  5  4
4  3  3
4  3  6
3  5  3
4  4  2
3  6  6
4  5  4
3  3  3
;

run;

Title "Overall"; run;
proc means n min mean max; format c codes. ; 
var math1 math1c math2; 
where (c=3 or c=4 );
run;

Title "By group"; run;
proc means n min mean max std; format c codes.; 
class c; var math1 math1c math2;
where (c=3 or c=4 );
run;