One option is to assign a SAS numeric variable and after sorting your file with PROC SORT and using a specific BY variable list, use a DATA step to assign the numeric sequence variable. You will need to look at using a BY statement in the DATA step and using IF FIRST. to reset your sequence variable as needed.
Suggest you search the SAS support http://support.sas.com/ website for DOC and supplemental technical reference and conference papers on the topic -- here is a Google advanced search argument to consider using: