Copy Mark value from a host to a hosted family

[M4RC1N]

Hello,

I am trying to write a script to do what is says above and manage to get to this point a shown in the pic below - i just cant figure out how to marry up the two lists - one of the hosts and the other of hosted elements - so we can copy value from the host onto hosted elements.

[Mike.Buttery]

This is the perfect use case for List.GroupByKey node

[M4RC1N]

Brilliant! Thanks Mike - it works like a charm