What should be the starting date of the first 12-month window for a customer id? is it the 1st of the month of the first record? Yes, For the sample data 01/01/2001 actual data set 01/01/1999 What should be the ending date of the last 12-month window? is it the end of the month of the last record for the id? actual data 12/31/2017 is it the end of the month 11 months after that last record? 12 months total so 11 months after the first month If you have an id in which the first and last records do not span 12 months, should that id be ignored? Yes, However, for the actual data the last rolling 12 month is 01/01/2017 to 12/31/2017, when I mapped it out in EXCEL assuming I did not make a mistake, it came out exactly through sheer dumb luck The output I'm looking for is a single table that should have 248 observations Periods Count M1 M248
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