Here below is the student data table:

Now we want to create a student ID for every student. The student ID should be: class number + student’s serial number in the class, and the serial number should be two-digit (calculate in cell C1):

=spl("=E(?1).group(Class).(~.(Class+string(#,""00""))).conj().new(~:ID)",A1:B21)

esProc Desktop and Excel Processing
7.14 Calculate proportion using aggregation information of data of the same group
8.1 Intersection, union and difference in the case of simple members - two sets