Create a new branch with input tree branches

[yingjie_wei]

Dear all:

I’d like to manipulate the tree branches like the tree->Draw() option:

tree->Draw(“jet_pt>>hist”,“(weight>0)*2*(event==1)”)

Is there a function or method of that: I’d like to create a new branch (not histogram) with the same number of events, based on the old tree branches. For example:

my_new_branch->FUNCTION(“jet_pt”,“(weight>0)*2*(event==1)”)

or

tree->FUNCTION(“jet_pt>>my_new_branch”,“(weight>0)*2*(event==1)”)

where jet_pt, weight and event are branches from the old tree(or input tree). and my_new_branch is the new branch (not histogram) I’d like to create with the same number of events as the old tree.

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Please read tips for efficient and successful posting and posting code

ROOT Version: 6.22.06
Platform: centos 7.9
Compiler: gcc 8.3.0

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[jblomer]

One way to do it is RDataFrame using the Define and Snapshot functions. Define adds a new (virtual) column to the data frame, and snapshot writes the result (old and new columns) to a new ROOT file. Roughly like this

ROOT::RDataFrame df("myTree", "myFile");
df_enhanced = df.Define("myBranch", "(weight > 0) * 2 * (event == 1)");
// Or possibly:
// df_enhanced = df.Define("myBranch", "jet_pt * (weight > 0) * 2 * (event == 1)");
df_enhanced.Snapshot("outputTree", "outputFile.root", "");

[yingjie_wei]

Hi Jblomer:

Thanks a lot! That’s great!

Cheers,
Yingjie