Logo ROOT   6.21/01
Reference Guide
tree3.C File Reference

Detailed Description

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

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.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.