If you would like something a bit more obscure and not subject to the issues of one id= 123 and another 321 in your data try the various bitwise logical functions if your ID is numeric.
For example look at
data _null_;
do x= 10 to 1010 by 10 ;
y = bnot(x);
z = bnot(y);
put y= z= ;
end;
run;
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