Hello BIMmers !
I wonder if we can join all the walls with all the slabs in once with Dynamo.
I tried doing it with this knode.
No succes yet. Would you have any advices to a lucky beginer ?
Many thanks in advance ! 
Erol
This will try to join every element to every other element (regardless of whether or not they’re even touching) and create a huge list of new, combined elements.
You’ll have to iterate through your lists if you want to end up with a single element on the other side, e.g. something like take one element, then check for intersections with the others, join those, and repeat for the remaining elements…
See also this post of someone else trying to do the same Elements Joining
Then what are trying to achieve if you don’t want to join geometries ? What is your expected output ?
Finally it works all fine with Revit 17 and Revit 18
Please indicate how you solved your problem so people with the same problem as you can easily find a solution in the future 
A I mentioned just before, It works but I dont know why it did not work before.
maybe thats because I’m a newbe and I make silly mistakes.
Just do the same knode as I did upper on my post.
Cheers to all !
Erol