Selecting certain events of a branch

ROOT
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I did something in one code that worked and I can’t get it to work in another.

Where it worked:

I have a file with many branches with information of many events, recently I was tasked with graphing the momentum of only the electrons, I did this and it worked:

tree->Draw("lepP4.Px()","lepPdgId>abs(11)");

For what I understand lepP4 has data of all leptons, and the branch Px has the momentum in the x direction of all leptons, and when I say “lepPdgId>abs(11)” it specifies that I only want electrons or antielectrons, since their identifiers are 11 and -11.

Where it doesn’t work yet:

I have to put that same data of momentum in a vector, and that is almost done:

// All libraries you could wish for
#include <iostream>                 // class for inputoutput streams
#include <stdio.h>                  // printf, scanf, puts, NULL
#include <stdlib.h>                 // srand, rand, atof
#include <time.h>                   // time
#include <fstream>                  // class for inputoutput file streams
#include <dirent.h>
#include <string.h>           // class to manipulate strings
#include <sstream>                    // class for parsing strings
#include <vector>


#include <TROOT.h>
#include <TChain.h>
#include <TFile.h>
#include <TH1F.h>
#include <TF1.h>
#include <TCanvas.h>
#include <TPaveStats.h>
#include <TPad.h>
#include <TMath.h>
#include <TStyle.h>
#include <TSystem.h>
#include <TLegend.h>
#include <TString.h>
#include <TGraph.h>
#include <TLatex.h>



#include <unistd.h>
#define GetCurrentDir getcwd

#include <TTree.h>
#include "Math/SMatrix.h"

using namespace std;
//  using namespace TMath;
int main(int argc, char* argv[])
{
  TFile* file = TFile::Open("/Users/Fer/Documents/traajo/samples/NeroNtuples_9.root"); // TFile::Open() instead of a constructor since it works over xrootd etc.
  TTree *tree=(TTree*)file->Get("nero/events");
  int nentries = tree->GetEntries(); // Get the number of entries
  ROOT::Math::SVector<double, 418886> px;
  double ievento; 
  tree->SetBranchAddress("lepP4.Px()","lepPdgId>abs(11)",&ievento); // Tell the tree which branch you want to be read into which variable

  for(int ientry = 0; ientry < nentries; ientry++) // Now you can loop over each entry in the TTree
  {
    tree->GetEntry(ientry); // Fetch the entry... this will change the value of variable1 and variable2
    // Do whatever you want with each event in here
    px[ientry]=ievento;
  }
  cout<<px;
  return 0;
}

That’s the whole code, and the problem lies on the SetBranchAddress method, because I wanted to specify that I wanted the electrons and antielectrons data in the same way but it doesn’t work, and I don’t know what to do, I’ve tried to read about the method but I can’t find what I need.

Thanks a lot

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