tree3.C File Reference

Detailed Description

Example of a Tree where branches are variable length arrays A second Tree is created and filled in parallel.

Run this script with

.x tree3.C

In the function treer, the first Tree is open. The second Tree is declared friend of the first tree. TTree::Draw is called with variables from both Trees.

#include "TFile.h"
#include "TTree.h"
#include "TRandom.h"
#include "TCanvas.h"

void tree3w() {

   const Int_t kMaxTrack = 500;
   Int_t ntrack;
   Int_t stat[kMaxTrack];
   Int_t sign[kMaxTrack];
   Float_t px[kMaxTrack];
   Float_t py[kMaxTrack];
   Float_t pz[kMaxTrack];
   Float_t pt[kMaxTrack];
   Float_t zv[kMaxTrack];
   Float_t chi2[kMaxTrack];
   Double_t sumstat;

   TFile f("tree3.root","recreate");
   TTree *t3 = new TTree("t3","Reconst ntuple");
   t3->Branch("ntrack",&ntrack,"ntrack/I");
   t3->Branch("stat",stat,"stat[ntrack]/I");
   t3->Branch("sign",sign,"sign[ntrack]/I");
   t3->Branch("px",px,"px[ntrack]/F");
   t3->Branch("py",py,"py[ntrack]/F");
   t3->Branch("pz",pz,"pz[ntrack]/F");
   t3->Branch("zv",zv,"zv[ntrack]/F");
   t3->Branch("chi2",chi2,"chi2[ntrack]/F");

   TFile fr("tree3f.root","recreate");
   TTree *t3f = new TTree("t3f","a friend Tree");
   t3f->Branch("ntrack",&ntrack,"ntrack/I");
   t3f->Branch("sumstat",&sumstat,"sumstat/D");
   t3f->Branch("pt",pt,"pt[ntrack]/F");

   for (Int_t i=0;i<1000;i++) {
      Int_t nt = gRandom->Rndm()*(kMaxTrack-1);
      ntrack = nt;
      sumstat = 0;
      for (Int_t n=0;n<nt;n++) {
         stat[n] = n%3;
         sign[n] = i%2;
         px[n]   = gRandom->Gaus(0,1);
         py[n]   = gRandom->Gaus(0,2);
         pz[n]   = gRandom->Gaus(10,5);
         zv[n]   = gRandom->Gaus(100,2);
         chi2[n] = gRandom->Gaus(0,.01);
         sumstat += chi2[n];
         pt[n]   = TMath::Sqrt(px[n]*px[n] + py[n]*py[n]);
      }
      t3->Fill();
      t3f->Fill();
   }
   t3->Print();
   f.cd();
   t3->Write();
   fr.cd();
   t3f->Write();
}

void tree3r()
{
   TFile *f = new TFile("tree3.root");
   TTree *t3 = (TTree*)f->Get("t3");
   t3->AddFriend("t3f","tree3f.root");
   t3->Draw("pz","pt>3");
}

void tree3r2()
{
   TPad *p = new TPad("p","p",0.6, 0.4, 0.98, 0.8);
   p->Draw(); p->cd();
   TFile *f1 = new TFile("tree3.root");
   TFile *f2 = new TFile("tree3f.root");
   TTree *t3 = (TTree*)f1->Get("t3");
   t3->AddFriend("t3f",f2);
   t3->Draw("pz","pt>3");
}

void tree3()
{
   tree3w();
   tree3r();
   tree3r2();
}

Author

Rene Brun

Definition in file tree3.C.