Ok, just as a last comment for  today:
Assume the following.. grid graph with shape 100x100
and a region adjacency graph with shape 10.
I want to accumulate features of rag.
Let's say user passes  grid graph node map with 3 channels => 100x100x Multiband(3).

No i want to reshape the  rag node map if empy....therefore i want a shape of 10x3.

Therefore I need to mix shapes.
Hope this was clear enough?