Tree 3

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.

Author: Rene Brun
This notebook tutorial was automatically generated with ROOTBOOK-izer (Beta) from the macro found in the ROOT repository on Tuesday, January 17, 2017 at 02:44 PM.



In [1]:

    
%%cpp -d
#include "TFile.h"
#include "TTree.h"
#include "TRandom.h"
#include "TCanvas.h"

A helper function is created:



In [2]:

    
%%cpp -d
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();
}

A helper function is created:



In [3]:

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

A helper function is created:



In [4]:

    
%%cpp -d
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");
}



In [5]:

    
tree3w();
tree3r();
tree3r2();









    



******************************************************************************
*Tree    :t3        : Reconst ntuple                                         *
*Entries :     1000 : Total =         7018667 bytes  File  Size =    4403660 *
*        :          : Tree compression factor =   1.55                       *
******************************************************************************
*Br    0 :ntrack    : ntrack/I                                               *
*Entries :     1000 : Total  Size=       4636 bytes  One basket in memory    *
*Baskets :        0 : Basket Size=      32000 bytes  Compression=   1.00     *
*............................................................................*
*Br    1 :stat      : stat[ntrack]/I                                         *
*Entries :     1000 : Total  Size=    1002099 bytes  File Size  =      16050 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=  60.65     *
*............................................................................*
*Br    2 :sign      : sign[ntrack]/I                                         *
*Entries :     1000 : Total  Size=    1002099 bytes  File Size  =      16427 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=  59.25     *
*............................................................................*
*Br    3 :px        : px[ntrack]/F                                           *
*Entries :     1000 : Total  Size=    1002032 bytes  File Size  =     903860 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=   1.08     *
*............................................................................*
*Br    4 :py        : py[ntrack]/F                                           *
*Entries :     1000 : Total  Size=    1002032 bytes  File Size  =     906967 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=   1.07     *
*............................................................................*
*Br    5 :pz        : pz[ntrack]/F                                           *
*Entries :     1000 : Total  Size=    1002032 bytes  File Size  =     870601 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=   1.12     *
*............................................................................*
*Br    6 :zv        : zv[ntrack]/F                                           *
*Entries :     1000 : Total  Size=    1002032 bytes  File Size  =     784206 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=   1.24     *
*............................................................................*
*Br    7 :chi2      : chi2[ntrack]/F                                         *
*Entries :     1000 : Total  Size=    1002106 bytes  File Size  =     905549 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=   1.07     *
*............................................................................*






    



Info in <TCanvas::MakeDefCanvas>:  created default TCanvas with name c1

Draw all canvases



In [6]:

    
gROOT->GetListOfCanvases()->Draw()