st: Stopping and Starting a Running Sum

[jasonm@ucla.edu]

I would like to create a running sum (eg SumHours) that restarts  
whenever there is a change in ID or the difference between the current  
date and previous day's date is >1.

ID  Hours    Date   SumHours
1    2      16437     2
1    3      16438     5
1    2      16440     2
1    2      16441     4
2    4      16437     4
2    3      16440     3
2    4      16441     7
2    2      16442     9
2    2      16443     11

Any ideas?

Thank  you.

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