Hello everyone, I discovered Dynamo this week and I love the potential it seems to have. I have zero experience with it but I am trying to grasp its concepts through trial and error using real life revit annoyances as small case studies. My first objective is that I would like to write the Unique ID of Walls which have the parameter ‘vdw-opdracht’ = “Yes” (a checkbox which I use to tell if a certain object is to be constructed by my firm). I have already set up my own instance parameter ‘unique ID’ for the wall instances. I have find nodes for ‘Categories’ (I chose Walls), then ‘All Elements of Category’. Then I think I should do ‘Elements.FilterByParameterValueAndCondition’ but I cannot get this to work. After this I am at a loss as to how to write the Unique ID to my wall instances… I would appreciate your help! Please let me know if I need to share more information to solve my first ever Dynamo test case 
Kind regards, René
Thank you for your reply! However, I get the following warnings, it did not set the parameters.
The first warning: Warning: “Internal error, please report: Dereferencing a non-pointer. (3f47aacd)”
The second warning: “Warning: Internal error, please report: Dereferencing a non-pointer. (3f47aacd)”
Also, is it possible to get all elements of MULTIPLE categories? As you can see in the attachment I would like to be able to get all elements of walls, ceilings and generic models…
Thanks again!
Never mind, my bad. I accidentally chose “bv Filter List by Mask” instead of “List.FilterByBoolMask”, whoops. No idea what the difference between the two is but now it works!
Nevertheless, I am still curious about my question about getting All elements of MULTIPLE categories!
Thanks!
Feed the 3 “AllElementsOfCategory” results into a “List.Join” node, then feed that into the elements port of GetParameter and Filter.
Works like a charm! I thought I tried it all. Thank you again.