Hi,
I think the conceptual issues described in the post you link are still present with a Filter(arr_flg) method in the scenarios in which upstream filters or Range calls are present.
If the arr_flg array describes a selection of entries over the whole dataset (no upstream filters/ranges) then transforming that array into a TEntryList and attaching it to the TTree/TChain is a viable workaround. Or indeed you can use a friend tree as Axel suggests.
Also see my errata at Adding data from an external container to a DataFrame - #15 by eguiraud
Cheers,
Enrico