Thank you for your help. Your code gives the 'first study dose taken'  dose values for all observation.  But I need most recent dose taken prior to aedate.   I modified your code. Please check if this is ok and let me know if anything wrong. Thanks   proc sql; create table one as select a.*,b.exdose,exdate,firstdosdt from AE as a left join EX_ as b on a.Subid=b.Subid and a.AEDATE-b.firstdosdt >0 and a.AEDATE-b.exdate >0 group by a.Subid,a.AEDATE having a.AEDATE-b.exdate=min(a.AEDATE-b.exdate); ; quit; ... View more

I am sorry for that insufficient information. I am again including all the information.   I need to flag last dose before the start of epoch='DOUBLE BLIND WITHDRAWAL'  dose( trtdate=28MAR2016.) For ID=1, the output needed is BASEFL='Y' for 4 th OBS. as it is last test  with (date1=2016-03-23)  before 28MAR2016.   For ID=2, since the trtdate is not avialable, first I need to subset all the OBS with 'date1' values less than date1 values when epoch='DOUBLE BLIND WITHDRAWAL'.  I need to subset first four OBS for ID=2, and then flag the last dose. The output needed is BASEFL='Y' for 4 th OBS for ID=2 Thanks you very much for your time.   data   id             test          date1                   epoch                                                                               trtdate 1            diabp         2016-01-26          SCREENING                                                             20FEB2016 1            diabp         2016-02-24           TITRATION                                                              20MAR2016 1           diabp          2016-03-09            TITRATION                                                             20MAR2016 1          diabp            2016-03-23           STABLE DOSE                                                       22MAR2016 1        diabp             2016-04-05            DOUBLE BLIND WITHDRAWAL                             28MAR2016 1        diabp             2016-04-08           DOUBLE BLIND WITHDRAWAL                              28APR2016     id             test          date1                   epoch                                                                               trtdate 2            diabp         2016-01-26          SCREENING                                                             2            diabp         2016-02-24           TITRATION                                                               2          diabp          2016-03-09            TITRATION                                                              2          diabp            2016-03-23           STABLE DOSE                                                      2        diabp             2016-04-05            DOUBLE BLIND WITHDRAWAL                             2        diabp             2016-04-08           DOUBLE BLIND WITHDRAWAL                                2        diabb             2016-05-08           FOLLOW-UP 2        diabb             2016-05-18           FOLLOW-UP   ... View more

Thank you very much. Your code worked. But in my dataset there are multiple AE dates for each subject. I am not getting the output all aedates.  Please look at second OBS. This is OBS is not seen in the output with your code. Thanks. Please help.    eg:    sub aedate 1 18FEB2016 1 16FEB2016 2 17JAN2016 3 01MAR2016   Output needed. Subid                       AEDATE                           Lastdose 1                               18FEB2016                       10 1                               16FEB2016                        5 2                               17JAN2016                         20 3                               01MAR2016                       20   ... View more

Thank you very much for the code. For your question, AEDATE=EXDATE when period =1 becuase with my code lastdose='dot' when aedate=exdate. I will look where I need to modify in your code to get my output. ... View more

Thank you very much for help. I created the following code. It produced the output I needed. But I want to know is there any mistake in it. Please provide your thoughts   if date1 ^= . then chardate1=put(date1,is8601da.); if compress(date2,'-') = : 'UNUNK' then chardate2= put(input(substr(compress(date2,'-'),6),best.),10.); else if compress(date2,'-') = : 'UN' then chardate3= put(input(substr(compress(date2,'-'),3),monyy7.),yymmd7.); if chardate1 ^= '' then chardate=chardate1; else if chardate2 ^= '' then chardate=chardate2; else if chardate3 ^= '' then chardate=chardate3; ... View more

Thanks for the suggestion . I need the Chardatevalue and output as mentioned. Please help. ... View more