Hi, Some documentation on "where=(...)" data set option: SAS(R) 9.4 Data Set Options: Reference In your example if b1 is numeric it should either be: a) "." (missing) b) "0" (zero) c) Any other number (e.g. 12, -77, etc.) (a) & (b) would be equivalent to False (observation would not be used) and (c) would be equivalent of True (observation will be used). E.g. the second data step uses "where=(age)" to only process a valid age value: data test1;   set sashelp.class;   if name=:'J' then     age=.; run; data test2;   set test1(where=(age)); run; Regards, Amir. ... View more