How to create comma-separated strings from grouped numbers?

Hello,

 

I have a list of around 1,000 numbers.
I would like to convert them into strings, with each string containing 20 numbers separated by commas.

I've already used the "Group by Number" component to create groups of 20 numbers each.
Now my question is: How can I convert these groups into comma-separated strings?

Thank you for your help!

 

Bernd