Hi, I have a data like the table below (also attached excel data). I need to create groupID by certain rules: 1. if locationID2 for previous row=locationID1 for the current row and if (intime for current row - outtime for previous <=1 ), then the rows are still put into the same group, e.g., groupID=1 2. Even if locationID2 for previous row not equal to locationID1 for the current row, as long as (intime for current row - outtime for previous <=1 ), then the rows are still put into the same group, e.g., groupID=2 3. Sometimes, there may be more than 2 cases in one group, e.g., groupID=3 4. Within the same person, groupID need to be in an increasing order 5. All other rows, groupID are assigned to be 0 Thanks for your help. person intime locationID outtime locationID2 groupID 1 2/17/2009 1 2/25/2009 0 0 1 3/14/2009 1 3/26/2009 0 0 1 5/21/2009 1 5/25/2009 0 0 1 6/6/2009 1 6/10/2009 0 0 1 6/19/2009 1 6/22/2009 4 1 1 6/22/2009 4 7/3/2009 0 1 1 7/11/2009 1 7/12/2009 6 2 1 7/12/2009 7 7/17/2009 0 2 1 8/5/2009 1 8/10/2009 0 0 1 5/6/2011 1 5/12/2011 0 0 1 8/10/2011 1 8/13/2011 3 3 1 8/13/2011 3 8/15/2011 7 3 1 8/15/2011 7 8/24/2011 0 3
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