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treefriend.C File Reference
Tutorials » Tree tutorials

Detailed Description

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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 = 100357 *
* : : Tree compression factor = 1.59 *
******************************************************************************
*Br 0 :Run : Run/I *
*Entries : 10000 : Total Size= 40698 bytes File Size = 262 *
*Baskets : 1 : Basket Size= 32000 bytes Compression= 122.13 *
*............................................................................*
*Br 1 :Event : Event/I *
*Entries : 10000 : Total Size= 40712 bytes File Size = 17634 *
*Baskets : 1 : Basket Size= 32000 bytes Compression= 1.81 *
*............................................................................*
*Br 2 :x : x/F *
*Entries : 10000 : Total Size= 40684 bytes File Size = 26767 *
*Baskets : 1 : Basket Size= 32000 bytes Compression= 1.20 *
*............................................................................*
*Br 3 :y : y/F *
*Entries : 10000 : Total Size= 40684 bytes File Size = 26662 *
*Baskets : 1 : Basket Size= 32000 bytes Compression= 1.20 *
*............................................................................*
*Br 4 :z : z/F *
*Entries : 10000 : Total Size= 40684 bytes File Size = 29032 *
*Baskets : 1 : Basket Size= 32000 bytes Compression= 1.10 *
*............................................................................*
******************************************************************************
*Tree :TF : test friend trees *
*Entries : 8460 : Total = 375780 bytes File Size = 144992 *
* : : Tree compression factor = 1.59 *
******************************************************************************
*Br 0 :Run : Run/I *
*Entries : 8460 : Total Size= 34463 bytes File Size = 371 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 91.57 *
*............................................................................*
*Br 1 :Event : Event/I *
*Entries : 8460 : Total Size= 34475 bytes File Size = 18880 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.80 *
*............................................................................*
*Br 2 :x : x/F *
*Entries : 8460 : Total Size= 34451 bytes File Size = 28500 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.19 *
*............................................................................*
*Br 3 :y : y/F *
*Entries : 8460 : Total Size= 34451 bytes File Size = 28389 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.20 *
*............................................................................*
*Br 4 :z : z/F *
*Entries : 8460 : Total Size= 34451 bytes File Size = 30521 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.11 *
*............................................................................*
nok = 8460, fentries=8460
#include "TTree.h"
#include "TFile.h"
#include "TRandom.h"
#include "TTree.h"
#include "TTree.h"
Int_t Run, Event;
Float_t x,y,z;
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;
}
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();
}
f
#define f(i)
Definition RSha256.hxx:104
fy
double fy() const
Int_t
int Int_t
Definition RtypesCore.h:45
Float_t
float Float_t
Definition RtypesCore.h:57
Long64_t
long long Long64_t
Definition RtypesCore.h:80
r
Option_t Option_t TPoint TPoint const char GetTextMagnitude GetFillStyle GetLineColor GetLineWidth GetMarkerStyle GetTextAlign GetTextColor GetTextSize void char Point_t Rectangle_t WindowAttributes_t Float_t r
Definition TGWin32VirtualXProxy.cxx:168
i
Int_t i
Definition TGraphAsymmErrors.cxx:1306
nentries
int nentries
Definition THbookFile.cxx:91
TDirectoryFile::Get
TObject * Get(const char *namecycle) override
Return pointer to object identified by namecycle.
Definition TDirectoryFile.cxx:937
TFile
A file, usually with extension .root, that stores data and code in the form of serialized objects in ...
Definition TFile.h:53
TFile::Open
static TFile * Open(const char *name, Option_t *option="", const char *ftitle="", Int_t compress=ROOT::RCompressionSetting::EDefaults::kUseCompiledDefault, Int_t netopt=0)
Create / open a file.
Definition TFile.cxx:4110
TRandom
This is the base class for the ROOT Random number generators.
Definition TRandom.h:27
TTree
A TTree represents a columnar dataset.
Definition TTree.h:79
TTree::CopyTree
virtual TTree * CopyTree(const char *selection, Option_t *option="", Long64_t nentries=kMaxEntries, Long64_t firstentry=0)
Copy a tree with selection.
Definition TTree.cxx:3719
TTree::Print
void Print(Option_t *option="") const override
Print a summary of the tree contents.
Definition TTree.cxx:7219
TTree::SetBranchAddress
virtual Int_t SetBranchAddress(const char *bname, void *add, TBranch **ptr=nullptr)
Change branch address, dealing with clone trees properly.
Definition TTree.cxx:8380
TTree::GetEntries
virtual Long64_t GetEntries() const
Definition TTree.h:466
TTree::GetEntryWithIndex
virtual Int_t GetEntryWithIndex(Int_t major, Int_t minor=0)
Read entry corresponding to major and minor number.
Definition TTree.cxx:5927
TTree::Write
Int_t Write(const char *name=nullptr, Int_t option=0, Int_t bufsize=0) override
Write this object to the current directory.
Definition TTree.cxx:9743
TTree::BuildIndex
virtual Int_t BuildIndex(const char *majorname, const char *minorname="0", bool long64major=false, bool long64minor=false)
Build a Tree Index (default is TTreeIndex).
Definition TTree.cxx:2637
TTree::SetName
void SetName(const char *name) override
Change the name of this tree.
Definition TTree.cxx:9195
y
Double_t y[n]
Definition legend1.C:17
x
Double_t x[n]
Definition legend1.C:17
Author
Rene Brun

Definition in file treefriend.C.