swh:1:snp:af87cd67498ef4fe47c76ed3e7caffe5b61facaf
Tip revision: 86108d5adde6979551fcbf3d95012f72653dd102 authored by Pere Mato on 03 March 2016, 09:36:03 UTC
Update ROOT version files to v6.06/02.
Update ROOT version files to v6.06/02.
Tip revision: 86108d5
tree1.C
/// \file
/// \ingroup tutorial_tree
/// This example is a variant of hsimple.C but using a TTree instead
/// of a TNtuple. It shows:
/// - how to fill a Tree with a few simple variables.
/// - how to read this Tree
/// - how to browse and analyze the Tree via the TBrowser and TTreeViewer
/// This example can be run in many different ways:
/// 1. Using the Cling interpreter
/// ~~~
/// .x tree1.C
/// ~~~
/// 2. Using the automatic compiler interface
/// ~~~
/// .x tree1.C++
/// ~~~
/// 3.
/// ~~~
/// .L tree1.C or .L tree1.C++
/// tree1()
/// ~~~
/// One can also run the write and read parts in two separate sessions.
/// For example following one of the sessions above, one can start the session:
/// ~~~
/// .L tree1.C
/// tree1r();
/// ~~~
/// \macro_code
///
/// \author Rene Brun
#include "TROOT.h"
#include "TFile.h"
#include "TTree.h"
#include "TBrowser.h"
#include "TH2.h"
#include "TRandom.h"
void tree1w()
{
//create a Tree file tree1.root
//create the file, the Tree and a few branches
TFile f("tree1.root","recreate");
TTree t1("t1","a simple Tree with simple variables");
Float_t px, py, pz;
Double_t random;
Int_t ev;
t1.Branch("px",&px,"px/F");
t1.Branch("py",&py,"py/F");
t1.Branch("pz",&pz,"pz/F");
t1.Branch("random",&random,"random/D");
t1.Branch("ev",&ev,"ev/I");
//fill the tree
for (Int_t i=0;i<10000;i++) {
gRandom->Rannor(px,py);
pz = px*px + py*py;
random = gRandom->Rndm();
ev = i;
t1.Fill();
}
//save the Tree header. The file will be automatically closed
//when going out of the function scope
t1.Write();
}
void tree1r()
{
//read the Tree generated by tree1w and fill two histograms
//note that we use "new" to create the TFile and TTree objects !
//because we want to keep these objects alive when we leave this function.
TFile *f = new TFile("tree1.root");
TTree *t1 = (TTree*)f->Get("t1");
Float_t px, py, pz;
Double_t random;
Int_t ev;
t1->SetBranchAddress("px",&px);
t1->SetBranchAddress("py",&py);
t1->SetBranchAddress("pz",&pz);
t1->SetBranchAddress("random",&random);
t1->SetBranchAddress("ev",&ev);
//create two histograms
TH1F *hpx = new TH1F("hpx","px distribution",100,-3,3);
TH2F *hpxpy = new TH2F("hpxpy","py vs px",30,-3,3,30,-3,3);
//read all entries and fill the histograms
Long64_t nentries = t1->GetEntries();
for (Long64_t i=0;i<nentries;i++) {
t1->GetEntry(i);
hpx->Fill(px);
hpxpy->Fill(px,py);
}
//we do not close the file. We want to keep the generated histograms
//we open a browser and the TreeViewer
if (gROOT->IsBatch()) return;
new TBrowser();
t1->StartViewer();
// in the browser, click on "ROOT Files", then on "tree1.root".
// you can click on the histogram icons in the right panel to draw them.
// in the TreeViewer, follow the instructions in the Help button.
}
void tree1() {
tree1w();
tree1r();
}