ALLSELECTED, but within the same visual

Hello,

I need to perform a string concatenation.

In my report, I have a single Deneb visual (running on vega-lite). Within its dataset, I want to add a column named 'Concatenation' to concatenate all values in 'Value to concatenate', for the selected rows (when I click on them), and appends the result to the dataset, no matter if this row is currently selected or not.

Here is the table in its basic state:

Here is the expected result when I select some of the rows (here in bold):

I tried some DAX formulas with ALLSELECTED, which doesn't seem to work when used within the same visual (but works very well when used on a separated table).

Maybe is there a solution in DAX, or in vega-lite (maybe using __selected__)?

Any help is greatly appreciated!