Count only distinct observation based in ID - data in long format

I have a dataset of a company events. An event can have many participants, that is why my data is a long format. There can be many rows for a single event. I just would like to create a frequency table of event types (outdoors vs indoor). I create a pivot table but since my data in a long format it is over-counting the event types. Please see the attach excel spreadsheet for more information.

Thank you very much in advance!
Marvin

Add a helper column to the data (needs to be sorted first)

In ex 2007 and younger are simple (formula - COUNTIFS) or create a table based on the data model. But for your release, you can do this by using columns of the auxiliary, which count uniques (unsorted source data).