I recently stumbled upon the nlevels function in SAS. It is awesome in terms of processing speed, given that the alternative is PROC SQL, COUNT(DISTINCT) etc etc
Truly the fastest way to find uniqueness in vars is use the nlevels in PROC FREQ – and why do we need to find levels in character variables- well to check for binary variables (2 values), constants (just 1 level), and simple data analysis stuff.
See this extract from-
ods output nlevels=levels;
proc freq data=good.sas nlevels;
tables _char_ /noprint;