You can run this tutorial with:
root > .x treefriend.C (interpreted via Cling)
root > .x treefriend.C+ (executed via ACLIC & the native compiler)or, variants like:
root > .L treefriend.C+
root > CreateParentTree();
root > CreateFriendTree();
root > CompareTrees();
root > DrawFriend();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 "TTree.h"
#include "TFile.h"
#include "TRandom.h"
#include "TTree.h"
#include "TTree.h"
Int_t Run, Event;
Float_t x,y,z;
A helper function is created:
In [2]:
%%cpp -d
void CreateParentTree() {
// create a simple TTree with 5 branches
// Two branches ("Run" and "Event") will be used to index the Tree
TFile *f = new TFile("treeparent.root","recreate");
TTree *T = new TTree("T","test friend trees");
T->Branch("Run",&Run,"Run/I");
T->Branch("Event",&Event,"Event/I");
T->Branch("x",&x,"x/F");
T->Branch("y",&y,"y/F");
T->Branch("z",&z,"z/F");
TRandom r;
for (Int_t i=0;i<10000;i++) {
if (i < 5000) Run = 1;
else Run = 2;
Event = i;
x = r.Gaus(10,1);
y = r.Gaus(20,2);
z = r.Landau(2,1);
T->Fill();
}
T->Print();
T->Write();
delete f;
}
A helper function is created:
In [3]:
%%cpp -d
void CreateFriendTree() {
// Open the file created by CreateParentTree
// Copy a subset of the TTree into a new TTree
// (see also tutorials copytree.C, copytree2.C and copytree3.C)
// Create an index on the new TTree ("Run","Event")
// Write the new TTree (including its index)
TFile *f = new TFile("treeparent.root");
TTree *T = (TTree*)f->Get("T");
TFile *ff = new TFile("treefriend.root","recreate");
TTree *TF = T->CopyTree("z<10");
TF->SetName("TF");
TF->BuildIndex("Run","Event");
TF->Write();
TF->Print();
delete ff;
}
A helper function is created:
In [4]:
%%cpp -d
void CompareTrees() {
// The two TTrees created above are compared.
// The subset of entries in the small TTree must be identical
// to the entries in the original TTree.
TFile *f = new TFile("treeparent.root");
TTree *T = (TTree*)f->Get("T");
TFile *ff = new TFile("treefriend.root");
TTree *TF = (TTree*)ff->Get("TF");
Int_t fRun,fEvent;
Float_t fx,fy,fz;
T->SetBranchAddress("Run",&Run);
T->SetBranchAddress("Event",&Event);
T->SetBranchAddress("x",&x);
T->SetBranchAddress("y",&y);
T->SetBranchAddress("z",&z);
TF->SetBranchAddress("Run",&fRun);
TF->SetBranchAddress("Event",&fEvent);
TF->SetBranchAddress("x",&fx);
TF->SetBranchAddress("y",&fy);
TF->SetBranchAddress("z",&fz);
T->AddFriend(TF);
Long64_t nentries = T->GetEntries();
Int_t nok = 0;
for (Long64_t i=0;i<nentries;i++) {
T->GetEntry(i);
if (fRun == Run && fEvent==Event && x==fx && y==fy &&z==fz) {
nok++;
} else {
if (TF->GetEntryWithIndex(Run,Event) > 0) {
if (i <100) printf("i=%lld, Run=%d, Event=%d, x=%g, y=%g, z=%g, : fRun=%d, fEvent=%d, fx=%g, fy=%g, fz=%g\n",i,Run,Event,x,y,z,fRun,fEvent,fx,fy,fz);
}
}
}
printf("nok = %d, fentries=%lld\n",nok,TF->GetEntries());
delete f;
delete ff;
}
A helper function is created:
In [5]:
%%cpp -d
void DrawFriend() {
// Draw a scatter plot of variable x in the parent TTree versus
// the same variable in the subtree.
// This should produce points along a straight line.
TFile *f = TFile::Open("treeparent.root");
TTree *T = (TTree*)f->Get("T");
T->AddFriend("TF","treefriend.root");
T->Draw("x:TF.x");
}
In [6]:
CreateParentTree();
CreateFriendTree();
CompareTrees();
DrawFriend();
Draw all canvases
In [7]:
gROOT->GetListOfCanvases()->Draw()