Assuming you had no class variables. You can this with proc summary or proc sql. Basically you output the results of a procedure as a SAS data set and merge back to your original dataset. The tricky part is merging the results back, see my simple examples below.
data mydataset;
input myvar;
datalines;
1
2
3
4
5
6
7
8
99
1000
;
run;
proc summary data=mydataset;
var myvar;
output out=summary_data (drop=_freq_ _type_)
mean(myvar)=mean_myvar;
run;
data newdata;
x=1;
set mydataset;
set summary_data point=x;
run;
* or use proc sql;
proc sql;
create table newdata as
select *, mean(myvar) as mean_myvar
from mydataset
;
quit;
Good Luck
-Darryl