Hi Nathan,

I've stumbled across across a research task that could really use yt's Boolean data object feature, and according to the documentation it is not implemented in yt-3.  Have boolean data objects been replaced by something else?  I know there are various filtering methods in yt, but what I really need to do is spatial filtering (i.e., data in a sphere with some chunks of the sphere excised).

This hasn't been implemented.

In principle I'd be happy to take a crack at re-implementing it, although I might need some help.  Could somebody give me a sense of why it wasn't ported to yt-3 when the changeover was made?

The data selection API was completely rewritten.

How difficult might it be to re-implement the boolean data objects in the new data selection API?  (I suppose the question is really "how difficult might it be for somebody who is a decent programmer but not an expert in yt's internals to do so"?)