SAS Visual Analytics - create parameter by aggregated measure

[Federicoconti01]

the problem:

If the user selects only one element as a filter, a calculation must be made on the table, otherwise if he selects no element or more than one, another calculated field is created.

I tried to solve:
     1. I created a field that calculates the number of selected elements.
      2. I created an if else:
          IF ( 'count_days'n = 1 )
          RETURN 1
          ELSE 0

I would like to create a parameter on the value of this calculated field to use on my main table