I have a long dataset with 1 to multiple (not fixed) rows per person_id. There are a number of variables but the ones of interest are person_id, start_date and end_date. The dataset is sorted according to person_id, start_date, end_date. I have identified an indicator case/s (flag=1) for each person_id. This may not be the first case (based on start_date) and an person_id may have none or multiple indicator cases. I would like to calculate the number of days between the end_date of the indicator case and each subsequent start_date until the next indicator within person_id or until next person_id. The below table shows the number of days column I would like to compute. person_id start_date end_date flag Number of days 1 02AUG2020 05AUG2020     1 08AUG2020 20AUG2020 1   1 10AUG2020 30AUG2020   -10 1 21AUG2020 21AUG2020   1 2 02AUG2020 05AUG2020     2 08AUG2020 10AUG2020 1   2 20AUG2020 21AUG2020   10 2 21AUG2020 21AUG2020 1   2 23AUG2020 31AUG2020   2 3 08AUG2020 10AUG2020     3 10AUG2020 21AUG2020     4 02AUG2020 05AUG2020 1   4 05AUG2020 21AUG2020   0 4 21AUG2020 24AUG2020   16 5 08AUG2020 10AUG2020     5 20AUG2020 21AUG2020 1     Thanks heaps in advance ... View more