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Update Entry in TTree branch

Hey everyone,

I’m a bit lost with “simple” root functions. I want to multiply all entries of a branch of a TTree with 1.24. Here is what I tried:

void HNL_modifyEfficiency(const char * fileName = "HNLNtuple.root", const char * treeName = "outTree") {

float eff;

TFile file(fileName,"READ");
TTree *tt = (TTree*)file.Get(treeName);

tt->SetBranchAddress("eff", &eff);

for(int i = 0; i < tt->GetEntries(); i++){
    tt->GetEntry(i);
    eff = eff * 1.24;
    tt->Fill();
}

TFile *ff = new TFile("HNLNtuple_plus1Sigma.root","recreate");
tt->Write();
ff->Close();
}

What am I doing wrong?

Cheers

Christian

This question was already asked on this forum, for instance here:

Thanks for the hint.

just to document it here again how I’ve done it:

TFile file(fileName,"READ");
TTree *inTree = (TTree*)file.Get(treeName);


TFile::Open("HNLNtuple_plus1Sigma.root","RECREATE");
TTree *outTree = new TTree("outTree", "outTree");

inTree -> SetBranchAddress("eff", &eff);

outTree -> Branch("eff", &effNew);

for(int i = 0; i < inTree->GetEntries(); i++){
    inTree->GetEntry(i);
    effNew = eff * 1.24;
    outTree->Fill();
}

outTree->Write();

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