Hello everyone, This problem bothered me a lot, could you have a look and advice on how I can solve this problem? thanks!   I have a dataset which has the structure as follows: ID is the customer ID that has default; open_month means = -60 means the bank account is opened before 60 months, the value of this column is from -60 to 0; MOB is the month on book, the value is from 0-60;   I'm trying to do a vintage analysis, so I need to calculate the accumulated number of default customers by open month and MOB, the structure of the output dataset should be open_month, MOB, count of accumulated distinct customer ID.   For example, for the combination of open_month = -60 and MOB = 10 should count all distinct ID where open_month = -60 and MOB <=10, hope I describe it clearly.     ID open_month MOB 5069216 -60 5 5069216 -60 6 5023640 -60 7 5023644 -60 7 5069216 -60 7 5069216 -60 9 5116761 -60 9 5069216 -60 10 5059854 -60 11 5069216 -60 11 5116761 -60 11 5002283 -60 12 5059854 -60 12 5069216 -60 12 5116761 -60 12 5059854 -60 13 5085886 -60 13 5116761 -60 13 5085886 -60 14 5116761 -60 14 5085886 -60 15 5085886 -60 16 5085886 -60 17 5085886 -60 18 5085886 -60 19 5085886 -60 20 5065314 -60 21 5085886 -60 21 5065314 -60 22 5085886 -60 22 5065314 -60 23 5085886 -60 23 5065314 -60 24 5085886 -60 24 5060452 -60 25 5065314 -60 25 5085886 -60 25   Your kindly help is highly appreciated!   Best Regards   Judy ... View more