Number of days since last event occurred

I've attached a sample file showing how my data looks.

I need a formula that calculates the number of days since an event occurred within the same group.

Example
I have my groups in Column A (Units or ICU)
Column B has the dates
Column C has a 1 or Null (1 if an event happen)
In Column D I need a formula that calculates the number of days since the group last had an event.

btw: my actual file has over 200K rows so VBA is OKay if anyone has a better way.

I hope my sample file makes since

Thanks

Originally Posted by Richard Buttrey

Hi,

Does the attached help

It works but can you help me understand the last IF function
=IF(AND($A10="Units",$C10=1),B10,IF(F9=0,0,F9))

How is it the cell above = 0
When it has a date in it?

Steve