Applying a filter

Question

https://code.sololearn.com/cka9M4wY2a6V/?ref=app

It takes notes of volunteers to work at a bar on certain positions to a chosen date.

The button "Terminvorschläge" (Opening suggestion) is to filter the list for all dates on which each workstation got a different number of volunteers (is at least chosen once, some workstations at least two times).
As a result, I want to show all entry's to all dates on which the conditions are fulfilled.

For filtering: No one picks a date to boolean it, the Programm should do so itself and give all possibilities.

There's this saying: I'm standing on a tube. (I'm lost)
Could someone help me out with (or Kickstart) the ActionEvent for the opening suggestions?

Thank you so much

Answer 1

Do you want display duplicate items, but only one item of each set of duplicity?