RDataFrame with Friend tree with TTreeIndex

I would like to create an RDataFrame for a nominal tree that has a friended particleLevel tree with a TTreeIndex built using the unique branch “eventNumber”. There are in general more events in the particleLevel tree than nominal, but all events contained in nominal are also contained in particleLevel. The entries in the trees are not already ordered by eventNumber.

As far as I can tell from reading through a related forum post and JIRA ticket, this functionality has not yet been implemented (but at least has a warning). Is there a plan to add this to an upcoming release?
ROOT Version: 6.20/02
Platform: centOS7
Compiler: gcc8

Hi @BrendonB,
and welcome to the ROOT forum!

I hear you, let me check the situation and get back to you asap.

Hi again,
I’m back with bad news unfortunately. TTreeReader, which RDataFrame uses internally for reading ROOT data, does not support indexed friend trees. Fixed that issue (which is high priority), RDataFrame should immediately be able to support indexed friend trees in single-thread runs. Multi-thread support will then possibly require some more work.

This means that the feature will not be present in the upcoming ROOT v6.22. Since last March especially, we are working our way through RDataFrame tickets (see a list here) and we did not get to friends+TTreeIndex in time.

Work in progress, sorry!

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