Modifying clone of TTree

[Andi1]

Hello there,

There is something that has been bothering me for some time. I want to clone a TTree and change some values. I work with GATE and I want to apply some post-processing, I know a workaround, that is creating a new tree and creating new branches manualy but how would one do this properly? Here is a minimal example:

#include <iostream>

#include "TFile.h"
#include "TTree.h"

using namespace std;

TFile * getTFile(const std::string filename, const string option);
void Set_Branch_Adresses(TTree *const current_tree, double& time);


int main()
{
    string treename("PhaseSpace"), filename_infile,
	filename_outfile("testfile.root");

    TFile *readfile_phase_out;
    TTree *readtree_phase_out;

    filename_infile = (string) "path/to/root/file";

    readfile_phase_out = getTFile(filename_infile, "READ");
    readtree_phase_out = (TTree*)readfile_phase_out->Get(treename.c_str());

    TFile* write_file = getTFile(filename_outfile, "Recreate");
    TTree* write_tree = readtree_phase_out->CloneTree();

    double time;
    Set_Branch_Adresses(write_tree, time);
    for (int i=0; i<10; i++)
    {
	write_tree->GetEntry(i);
	cout << time << endl;
	time = 1;  // <- Value is not changing
    }

    cout << endl << endl;

    for (int i=0; i<10; i++)
    {
	write_tree->GetEntry(i);
	cout << time << endl; // nothing changed
    }
}


void Set_Branch_Adresses(TTree *const current_tree, double& time)
{
    current_tree->SetBranchAddress("Time", &time);
}

TFile * getTFile(const string filename, const string option)
{
    TFile *file = new TFile(filename.c_str(), option.c_str());

    if (!file->IsOpen())
    {
        cerr << "Could Not open Inputfile: " << filename << endl;
        exit(1);
    }
    return file;
}

1. How can I change the value of time in the cloned tree?
2. Why exactly is this not working?

Cheers,
Andi

---

_ROOT Version: 6.18/04
_Platform: Ubuntu 18.04
_Compiler: gcc 7.5

---

[pcanal]

You would do something similar to: https://root.cern/doc/master/copytree3_8C.html
where instead of filtering entries, you would SetBranchAddress on the data you need to update and modify it between the GetEntry and Fill.