Accessing branches

[sanjeeda]

__I have a root file whose contents are arranged as shown. I need to access The leaf MCParticles.m_pdg and put a cut on it. I am trying as follows but I am not able to get it. Would you please help?

void Dtorhog_problem()
{

   TFile *f = new TFile("Dtorhog_sim_my20K.root");
   TTree *tree = (TTree*)f->Get("tree/MCParticles/");

   Int_t MCParticles, MCParticles.m_pdg, MCParticles.m_firstDaughter, MCParticles.m_lastDaughter ;

   //  tree->SetBranchAddress("MCParticles",&MCParticles);
   tree->SetBranchAddress("MCParticles.m_pdg",&MCParticles.m_pdg);
   tree->SetBranchAddress("MCParticles.m_firstDaughter",&MCParticles.m_firstDaughter);
   tree->SetBranchAddress("MCParticles.m_lastDaughter",&MCParticles.m_lastDaughter);


   //create  histograms
   TH1F *h1 = new TH1F("First Daughters","First Daughters",100, -500, 500);
   // TH1F *h2 = new TH1F("#pi^{0}","Invariant Mass of #pi^{0}",100, 0.124, 0.140);


   Int_t nentries = (Int_t)tree->GetEntries();
   for (Int_t i=0; i<nentries; i++) {
      tree->GetEntry(i);
      if(MCParticles.m_pdg==433)
      {
         h1->Fill(MCParticles.m_firstDaughter);
         h1->GetXaxis()->SetTitle("First Daughter");

      }

      if (gROOT->IsBatch()) return;
      new TBrowser();
   }

}

ROOT Version: Not Provided
Platform: Not Provided
Compiler: Not Provided

---

[Pnine]

Hello,

have you thought to a declarative approach via RDataFrame?
The syntax for your task would be:

ROOT::RDataFrame rdf("Dtorhog_sim_my20K.root","tree/MCParticles");
auto h = rdf.Filter("MCParticles.m_pdg==433").Define("first_daughter","MCParticles.m_firstDaughter").Histo1D("first_daughter");
h->GetXaxis()->SetTitle(“First Daughter”);
if (gROOT->IsBatch()) return;
new TBrowser();

Cheers,
P

[sanjeeda]

Thank you so much. I had never tried this before. As per your suggestion , I am trying to use the following code:

void Dtorhog_problem()
{

   TFile *f = new TFile("Dtorhog_sim_my20K.root");
   TTree *tree = (TTree*)f->Get("tree/MCParticles/");

   Int_t MCParticles, MCParticles.m_pdg, MCParticles.m_firstDaughter, MCParticles.m_lastDaughter ;

   tree->SetBranchAddress("MCParticles",&MCParticles);
   tree->SetBranchAddress("MCParticles/MCParticles.m_pdg",&MCParticles/MCParticles.m_pdg);
   tree->SetBranchAddress("MCParticles/MCParticles.m_firstDaughter",&MCParticles/MCParticles.m_firstDaughter);
   tree->SetBranchAddress("MCParticles/MCParticles.m_lastDaughter",&MCParticles/MCParticles.m_lastDaughter);
   ROOT::RDataFrame rdf("Dtorhog_sim_my20K.root","tree/MCParticles");
   auto h = rdf.Filter("MCParticles.m_pdg==433").Define("first_daughter","MCParticles.m_firstDaughter").Histo1D("first_daughter");
   h->GetXaxis()->SetTitle(“First Daughter”);
   if (gROOT->IsBatch()) return;
   new TBrowser();
}

However, when I try to run, I get the error message:“illegal pointer to class object tree 0x0 1105 Dtorhog_problem.C:9:”. Now this is an error which is received when the path is wrong. Here, the path to the leaf is correct. What could be the reason?

[pcanal]

@sanjeeda

“illegal pointer to class object tree 0x0 1105 Dtorhog_problem.C:9:”.

This indicates that the Get command is not finding the tree.
To get some more information try:

TFile *f = new TFile("Dtorhog_sim_my20K.root");
TTree *tree = (TTree*)f->Get("tree/MCParticles/");
if (tree == nullptr) {
   cerr << "Could not find the tree using the name 'tree/MCParticles/'.  Let look at the file content:\n";
   file->ls();
   return;
}

[sanjeeda]

Thanks a lot. I had tried the following code but i receive "Break Segmentation Violation "

void fixed()
{
   TFile *file=new TFile("Dtorhog_sim_my20K.root");
   
   TTree *tr=(TTree*)file->Get("tree");
   
   TLeaf *l1=(TLeaf*)tr->GetLeaf("MCParticles.m_pdg");
  
 //The histograms:
   TH1F* h1 = new TH1F("Particles", " ", 100,400,450);
 
   Int_t pdgcode;

  Int_t  nentries = (Int_t)tr->GetEntries();
 //cout<<"entries from tree"<<"        "<<nentries<<"\n";                                                                                                               
  for(Int_t i=0;i<nentries;i++){
        tr->GetEntry(i);
 
cout<<"len1"<<" "<<l1->GetLen()<<endl;
       
        Int_t len1;
       	len1 = l1->GetLen();//Return the number of effective elements of this leaf, for the current entry. 
     	cout<<len1<<"\t"<<endl;                                                            

     	for(Int_t m=0; m< len1; m++)
      		{
        	pdgcode = l1->GetValue(m); 
        //cout<<l1->GetValue(m)<<endl;
       		// if (pdgcode==431)
       		  //{
     		     h1->Fill(pdgcode);
  			//  }
			//}
		   			}
h1->Draw();	
		
  }
}