//Example illustrating how to save histograms in Tree branches.
//To run this example, do
// root > .L htest.C
// root > htw()
// root > htr1()
// root > htr2()
// root > htr3()
void htw() {
//create a Tree with a few branches of type histogram
//25000 entries are filled in the Tree
//For each entry, the copy of 3 histograms is written
//The data base will contain 75000 histograms.
gBenchmark->Start("hsimple");
TFile f("ht.root","recreate");
TTree *T = new TTree("T","test");
TH1F *hpx = new TH1F("hpx","This is the px distribution",100,-4,4);
TH2F *hpxpy = new TH2F("hpxpy","py vs px",40,-4,4,40,-4,4);
TProfile *hprof = new TProfile("hprof","Profile of pz versus px",100,-4,4,0,20);
T->Branch("hpx","TH1F",&hpx,32000,0);
T->Branch("hpxpy","TH2F",&hpxpy,32000,0);
T->Branch("hprof","TProfile",&hprof,32000,0);
Float_t px, py, pz;
for (Int_t i = 0; i < 25000; i++) {
if (i%1000 == 0) printf("at entry: %d\n",i);
gRandom->Rannor(px,py);
pz = px*px + py*py;
hpx->Fill(px);
hpxpy->Fill(px,py);
hprof->Fill(px,pz);
T->Fill();
}
T->Print();
f.Write();
gBenchmark->Show("hsimple");
}
void htr1() {
//connect Tree generated by htw and show histograms for entry 12345
TFile *f = new TFile("ht.root");
TTree *T = (TTree*)f->Get("T");
TH1F *hpx = 0;
TH2F *hpxpy = 0;
TProfile *hprof = 0;
T->SetBranchAddress("hpx",&hpx);
T->SetBranchAddress("hpxpy",&hpxpy);
T->SetBranchAddress("hprof",&hprof);
T->GetEntry(12345);
TCanvas *c1 = new TCanvas("c1","test",10,10,600,1000);
c1->Divide(1,3);
c1->cd(1);
hpx->Draw();
c1->cd(2);
hpxpy->Draw();
c1->cd(3);
hprof->Draw();
}
void htr2() {
//connect Tree generated by htw and show histograms for entry 12345
// a variant of htr1
TFile *f = new TFile("ht.root");
TTree *T = (TTree*)f->Get("T");
TCanvas *c1 = new TCanvas("c1","test",10,10,600,1000);
c1->Divide(1,3);
c1->cd(1);
T->Draw("hpx.Draw()","","goff",1,12345);
c1->cd(2);
T->Draw("hpxpy.Draw()","","goff",1,12345);
c1->cd(3);
T->Draw("hprof.Draw()","","goff",1,12345);
}
void htr3() {
//connect Tree generated by htw
//read all histograms and plot the RMS of hpx versus the Mean of hprof
//for each of the 25000 entries
TFile *f = new TFile("ht.root");
TTree *T = (TTree*)f->Get("T");
T->Draw("hpx.GetRMS():hprof.GetMean()");
}