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Reference Guide
treefriend.C File Reference

Detailed Description

View in nbviewer Open in SWAN Illustrates how to use Tree friends:

  • create a simple TTree
  • Copy a subset of this TTree to a new TTree
  • Create a Tree Index
  • Make a friend TTree
  • compare two TTrees
  • Draw a variable from the first tree versus a variable in the friend Tree

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();
******************************************************************************
*Tree :T : test friend trees *
*Entries : 10000 : Total = 203762 bytes File Size = 94821 *
* : : Tree compression factor = 1.69 *
******************************************************************************
*Br 0 :Run : Run/I *
*Entries : 10000 : Total Size= 40698 bytes File Size = 265 *
*Baskets : 1 : Basket Size= 32000 bytes Compression= 120.75 *
*............................................................................*
*Br 1 :Event : Event/I *
*Entries : 10000 : Total Size= 40712 bytes File Size = 11231 *
*Baskets : 1 : Basket Size= 32000 bytes Compression= 2.85 *
*............................................................................*
*Br 2 :x : x/F *
*Entries : 10000 : Total Size= 40684 bytes File Size = 27116 *
*Baskets : 1 : Basket Size= 32000 bytes Compression= 1.18 *
*............................................................................*
*Br 3 :y : y/F *
*Entries : 10000 : Total Size= 40684 bytes File Size = 27035 *
*Baskets : 1 : Basket Size= 32000 bytes Compression= 1.18 *
*............................................................................*
*Br 4 :z : z/F *
*Entries : 10000 : Total Size= 40684 bytes File Size = 29174 *
*Baskets : 1 : Basket Size= 32000 bytes Compression= 1.10 *
*............................................................................*
******************************************************************************
*Tree :TF : test friend trees *
*Entries : 8460 : Total = 375780 bytes File Size = 128540 *
* : : Tree compression factor = 1.69 *
******************************************************************************
*Br 0 :Run : Run/I *
*Entries : 8460 : Total Size= 34463 bytes File Size = 374 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 90.84 *
*............................................................................*
*Br 1 :Event : Event/I *
*Entries : 8460 : Total Size= 34475 bytes File Size = 12152 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 2.80 *
*............................................................................*
*Br 2 :x : x/F *
*Entries : 8460 : Total Size= 34451 bytes File Size = 28849 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.18 *
*............................................................................*
*Br 3 :y : y/F *
*Entries : 8460 : Total Size= 34451 bytes File Size = 28757 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.18 *
*............................................................................*
*Br 4 :z : z/F *
*Entries : 8460 : Total Size= 34451 bytes File Size = 30674 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.11 *
*............................................................................*
nok = 8460, fentries=8460
pict1_treefriend.C.png
#include "TTree.h"
#include "TFile.h"
#include "TRandom.h"
#include "TTree.h"
#include "TTree.h"
Int_t Run, Event;
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");
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;
}
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;
}
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;
}
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");
}
void treefriend() {
CreateParentTree();
CreateFriendTree();
CompareTrees();
DrawFriend();
}
Author
Rene Brun

Definition in file treefriend.C.