Measure showing all existing rows

Hello, 

I've recently ran into the problem based on not founding possibility to show every existing row in given column in a way that everything will be listed after the commas. 

For example, I would like to have sources in one country listed after each other and not as the different rows in this visual. So the output would be just:

Is there a possibilty to somehow programm it like that? I found till this moment a function DISTINCT but the visual crashes after I try to use it so I guess it wont work in that case.

Thank you in advance!