TTree friend just for some entries

[LeWhoo]

I can’t share the TTree Print() output yet, because the TTrees are under construction. Everything is related to this post:

The optimal way to store variable tracks count in a TTree

Hello, As I have mentioned in this post: Array of strings as a leaf in a branch of TTree I am trying to find out if we can replace our HDF5 structure with ROOT and gain significant speed. The main issue is that in our events we have a variable number of tracks. Each track consists of x, y and z arrays (and corresponding 3 arrays for something else), whose length varies between tracks (although is the same inside a single track). I am benchmarking on a TTree with 1000 events. Initially, I’ve …

and we’ve (finally?) decided to try with ROOT instead of HDF5. Good support on this forum is one of the reasons
The initial idea with HDF5 was to add variables to Events as they passed reconstruction stages. This is not optimal (close to impossible) with ROOT TTrees, but the “friends” approach is more appealing for me. Most likely the fraction of reconstructible events during the prototype phase of the experiment will be very small. However, it could change significantly in next phases that will come in several years. Is there any estimate what is the overhead of using TTreeIndex?