Hi MKPK, Does this do what you are after? DATA HAVE; INFILE DATALINES DELIMITER=','; INPUT USUBJID $ MONTH $ TREATMENTS $; DATALINES; USUBJID1,01,DRUG USUBJID1,02,PLACEBO USUBJID1,03,DRUG USUBJID1,04,DRUG USUBJID1,05,DRUG USUBJID1,06,DRUG USUBJID1,07,DRUG USUBJID1,08,DRUG USUBJID1,09,DRUG USUBJID1,10,DRUG USUBJID1,11,DRUG USUBJID1,12,DRUG ; RUN; PROC SORT DATA=HAVE; BY USUBJID MONTH; RUN; DATA WANT; MERGE HAVE (IN=A WHERE=(PTREATMENTS = "PLACEBO") RENAME = (MONTH = PMONTH TREATMENTS = PTREATMENTS)) HAVE (IN=B); BY USUBJID; IF A AND B AND MONTH > PMONTH; DROP PMONTH PTREATMENTS; RUN;
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