Example Page

Merging

This example shows a simple way to merge the root tree files or to use the root tree files made by the previous example to make histograms. The example to download will allow you to add as may histogram as you like in a header file named test.h. If you would like to put result in a file instead you can do something like the following (run these on the previous example out put file called output.root).

Skim trees into a new file

int main(int __argc,char *__argv[]){
   char *outFileName = "mergeout.root";
   extern int optind;   
   TROOT troot();  
   TFile outFile(outFileName,"recreate");  
   
   Float_t P1_x,P1_y,P1_z,P1_e,P2_x,P2_y,P2_z,P2_e,P3_x,P3_y,P3_z,P3_e,e_gamma;
   
   TH1F *plot_1 = new TH1F("plot_1","test",200,0,2);    
   TH2F *plot_2 = new TH2F("plot_2","test",100,0,2,100,0,2);

for(int n_arg = optind; n_arg < __argc; n_arg++){   
   TFile inFile(__argv[n_arg]); // open the input file         
   
   if( TTree *p0 = (TTree*)inFile.Get("p0")){
      
   p0->SetBranchAddress("P1_x",&P1_x);
   p0->SetBranchAddress("P1_y",&P1_y);
   p0->SetBranchAddress("P1_z",&P1_z);
   p0->SetBranchAddress("P1_e",&P1_e);
   p0->SetBranchAddress("P2_x",&P2_x);
   p0->SetBranchAddress("P2_y",&P2_y);
   p0->SetBranchAddress("P2_z",&P2_z);
   p0->SetBranchAddress("P2_e",&P2_e);
   p0->SetBranchAddress("P3_x",&P3_x);
   p0->SetBranchAddress("P3_y",&P3_y);
   p0->SetBranchAddress("P3_z",&P3_z);
   p0->SetBranchAddress("P3_e",&P3_e);
   p0->SetBranchAddress("e_gamma",&e_gamma);
    
   TLorentzVector P4pho,P4_1,P4_2,P4_3,P4target,P4tot,P4mis;
  
   Int_t nentries = (Int_t)p0->GetEntries();  
   for (Int_t j=0;j<=nentries;j++) { p0->GetEntry(j);
  	  P4target.SetPxPyPzE(0.0,0.0,0.0,0.93828);
  	  P4pho.SetPxPyPzE(0.,0.,e_gamma,e_gamma);
	  P4_1.SetPxPyPzE(P1_x, P1_y, P1_z, P1_e);
	  P4_2.SetPxPyPzE(P2_x, P2_y, P2_z, P2_e);
	  P4_3.SetPxPyPzE(P3_x, P3_y, P3_z, P3_e);	  
	  	  	  	  
	  P4tot = P4target+P4pho;
	  P4mis = P4tot-(P4_1+P4_2+P4_3);
	  plot_1->Fill(P4mis.M());
	  plot_2->Fill(P4mis.M(),P4mis.P());
	  
  }//for
  }//if
  	else {
            cout << "File has no TTree named p0 or does not exist!!" << endl;
        }  
  }//n_arg
  
     outFile.Write(); // write to the output file
     outFile.Close(); // close the output file

}//end of main

If instead you make a new tree instead of histograms you can make sequential skims of you data set. In this way you can merge various trees into a single storage tree.