Index of selected item

[xxx]

Hi, I have to lists with equal length, e.g. date list and location list.
I want to use the date list to put it into a Eingabedialog as an Einfachauswahl.
If I select the 3rd date in the list, I need the position stored in a variable to get the 3rd item of the location list with an already existing function.
Would that be possible?

Thanks.