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 from the macro found in the ROOT repository on Monday, February 17, 2020 at 04:09 AM.

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 =         7018766 bytes  File  Size =    4403660 *
*        :          : Tree compression factor =   1.55                       *
******************************************************************************
*Br    0 :ntrack    : ntrack/I                                               *
*Entries :     1000 : Total  Size=       4647 bytes  One basket in memory    *
*Baskets :        0 : Basket Size=      32000 bytes  Compression=   1.00     *
*............................................................................*
*Br    1 :stat      : stat[ntrack]/I                                         *
*Entries :     1000 : Total  Size=    1002090 bytes  File Size  =      16050 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=  60.65     *
*............................................................................*
*Br    2 :sign      : sign[ntrack]/I                                         *
*Entries :     1000 : Total  Size=    1002090 bytes  File Size  =      16427 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=  59.25     *
*............................................................................*
*Br    3 :px        : px[ntrack]/F                                           *
*Entries :     1000 : Total  Size=    1002023 bytes  File Size  =     903860 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=   1.08     *
*............................................................................*
*Br    4 :py        : py[ntrack]/F                                           *
*Entries :     1000 : Total  Size=    1002023 bytes  File Size  =     906967 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=   1.07     *
*............................................................................*
*Br    5 :pz        : pz[ntrack]/F                                           *
*Entries :     1000 : Total  Size=    1002023 bytes  File Size  =     870601 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=   1.12     *
*............................................................................*
*Br    6 :zv        : zv[ntrack]/F                                           *
*Entries :     1000 : Total  Size=    1002023 bytes  File Size  =     784206 *
*Baskets :       31 : Basket Size=      32000 bytes  Compression=   1.24     *
*............................................................................*
*Br    7 :chi2      : chi2[ntrack]/F                                         *
*Entries :     1000 : Total  Size=    1002097 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()