Fill existing tree in pyroot

[ROOTer1]

I was wondering how you can fill events in an existing tree, I was trying something like this:

#first make a new one

subtree = ROOT.TTree(“subtree”,“subtree”)
subtree.Branch(“var1” ,get_var1)
subtree.Branch(“var2” ,get_var2)
subtree.Write()

#later in an event loop

subtree = ROOT.gDirectory.Get(“subtree”)
get_var1 = var1_value_for_event_i
get_var2 = var2_value_for_event_i
subtree.Fill()

but this gives the following error:
Error in TBranchElement::Fill: attempt to fill branch var1 while addresss is not set
Error in TBranchElement::Fill: attempt to fill branch var2 while addresss is not set

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[etejedor]

Hello,
I will answer in the original thread:

Filling different trees in a loop in pyroot

Hello, The most efficient way to do this would be to use RDataFrame: With RDataFrame, the loop would happen in C++, and therefore the performance would be better than to have it in Python. As for what you want to do, the way to proceed would be to create an RDataFrame from your initial tree stored in your ROOT file. From that tree, you can define new columns (branches) based on the information contained in the initial tree. Finally, you can Snapshot (store in a file) the derived trees. In …