You have at least two possible approaches depending on how you will actually use the the out dataset, change the value which will be data step, or a format so the displayed value is blank.
/* to actually change the value*/
data out1;
set out;
call missing (subject);
run;
/* missing may be represented by other characters than .
to show blank*/
options missing=' ';
proc print data=out1 noobs;
var block treatment subject;
run;
options missing='.';
/* or use a format to change the display*/
proc format library=work;
value blank
low-high=' '
;
run;
proc print data=out noobs;
var block treatment subject;
format subject blank.;
run;
If you are going to do this frequently then the format approach may be preferred if using the proc print output. Otherwise use the data change.
... View more