Replace/Map skip list items with "N/A" or other place holder

I like to learn more list logic tricks. I end up with a problem that seems I can have it done by some simple List nodes but end up with by using Python Script.
Just for example I have level from Level 1 to Level 10 but not every level has beams belongs to it. for level has no beam I want to show “N/A” on the list output. I’m wondering is there any built-in nodes can make this result?

The reason you’re having trouble is because you’re using a list of booleans (0/1 in your case) and trying to map that to your filtered list. You need to compare it with your original list since that’s where the booleans come from. This makes things much easier.

Thank you
but what happen if link the “true” input to the removed Item list? This is the list with collected data in it.

Ah. I’m sorry, I misread your graph the first time.
The If node requires matching list lengths for the True and False outputs. It also requires that each input and output match up. It also doesn’t handle different list structures well. Python is probably your best bet in this case.

Thanks Nick
sorry that It is hard for me to describe the desire result sometimes due to my second language problem. but there are all ways tricks that I can steal form any reply.