Generating two trees and saving one in a file

ROOT
1

Hello

I generated two trees and tried to save only one tree in a root file.
When I opened the file, I found the tree was saved as I intended.
But the problem is the size of the file. The size of the root file is
much bigger than I expected (the tree I saved has only 100 entries having
just one branch) and it seems like the other tree affected the size
of the root file, too. Please help me understand this file size issue.
I am attaching my test code.

Thanks,
SC

{
  TFile *af = new TFile("ttree_test.root","recreate");
   TTree *tr = new TTree("tr","tr");
   TTree *trb = new TTree("trb","trb");

   double x1,y1,z1;
   double x1b;
   int ient;
   int ii,jj;
   tr->Branch("x1",&x1,"x1/D");
   tr->Branch("y1",&y1,"y1/D");
   tr->Branch("z1",&z1,"z1/D");

   trb->Branch("x1b",&x1b,"x1b/D");
   TRandom3 r;
   
  for(jj=0;jj<100;jj++)
  {
   for(ii=0;ii<10000;ii++)
   {
     //if(ii%100==0)cout<<ii<<endl;
     x1= r.Gaus(10,3);
     y1= r.Gaus(-2,1);
     z1= r.Gaus(4,0.5);
     ient = ii;
     tr->Fill();
    }

   TH1F *h1 = new TH1F("h1","h1",100,0,24);
   tr->Project("h1","x1+y1","z1>4");
   x1b = h1->GetMean();
   cout<<x1b<<endl;
   trb->Fill();
   tr->Reset();
   h1->Reset();
  } 

    trb->Write();
    af->Close();
}
2 
{
  TFile *af = new TFile("ttree_test.root","recreate");
  TTree *trb = new TTree("trb","trb"); // disk resident
  gROOT->cd();
  TTree *tr = new TTree("tr","tr"); // memory resident
  
  double x1,y1,z1;
  double x1b;
  int ient;
  int ii,jj;
  tr->Branch("x1",&x1,"x1/D");
  tr->Branch("y1",&y1,"y1/D");
  tr->Branch("z1",&z1,"z1/D");
  
  trb->Branch("x1b",&x1b,"x1b/D");
  TRandom3 r;
  
  for(jj=0;jj<100;jj++)
    {
      for(ii=0;ii<10000;ii++)
        {
          //if(ii%100==0)cout<<ii<<endl;
          x1= r.Gaus(10,3);
          y1= r.Gaus(-2,1);
          z1= r.Gaus(4,0.5);
          ient = ii;
          tr->Fill();
        }
      
      TH1F *h1 = new TH1F("h1","h1",100,0,24);
      tr->Project("h1","x1+y1","z1>4");
      x1b = h1->GetMean();
      cout<<x1b<<endl;
      trb->Fill();
      tr->Reset();
      delete h1; // not used any more
    }
  
  delete tr; // not used any more
  
  af->Write();
  delete af; // automatically deletes "trb", too
}
3

Thanks for the reply.
This is working.
By the way, can you explain the meaning of the line " gROOT->cd()"?

SC

4

TDirectory::cd
ROOT User’s Guide -> Input/Output -> The Logical ROOT File: TFile and TKey -> The Current Directory
ROOT User’s Guide -> Input/Output -> The Logical ROOT File: TFile and TKey -> Objects in Memory and Objects on Disk