TTreeReader is a simple, robust and fast interface to read values from a TTree, TChain or TNtuple.

It uses TTreeReaderValue<T> and TTreeReaderArray<T> to access the data.

Example code can be found in tutorials/tree/hsimpleReader.C and tutorials/trees/h1analysisTreeReader.h and tutorials/trees/h1analysisTreeReader.C for a TSelector.

Roottest contains an example showing the full power.

A simpler analysis example - the one from the tutorials - can be found below: it histograms a function of the px and py branches.

// A simple TTreeReader use: read data from hsimple.root (written by hsimple.C)
#include "TFile.h
#include "TH1F.h
#include "TTreeReader.h
#include "TTreeReaderValue.h
void hsimpleReader() {
   // Create a histogram for the values we read.
   TH1F("h1", "ntuple", 100, -4, 4);
   // Open the file containing the tree.
   TFile *myFile = TFile::Open("$ROOTSYS/tutorials/hsimple.root");
   // Create a TTreeReader for the tree, for instance by passing the
   // TTree's name and the TDirectory / TFile it is in.
   TTreeReader myReader("ntuple", myFile);
   // The branch "px" contains floats; access them as myPx.
   TTreeReaderValue<Float_t> myPx(myReader, "px");
   // The branch "py" contains floats, too; access those as myPy.
   TTreeReaderValue<Float_t> myPy(myReader, "py");
   // Loop over all entries of the TTree or TChain.
   while (myReader.Next()) {
      // Just access the data as if myPx and myPy were iterators (note the '*'
      // in front of them):
      myHist->Fill(*myPx + *myPy);
   }
   myHist->Draw();
}

A more complete example including error handling and a few combinations of TTreeReaderValue and TTreeReaderArray would look like this:

#include <TFile.h>
#include <TH1.h>
#include <TTreeReader.h>
#include <TTreeReaderValue.h>
#include <TTreeReaderArray.h>
#include "TriggerInfo.h"
#include "Muon.h"
#include "Tau.h"
#include <vector>
#include <iostream>
bool CheckValue(ROOT::TTreeReaderValueBase* value) {
   if (value->GetSetupStatus() < 0) {
      std::cerr << "Error " << value->GetSetupStatus()
                << "setting up reader for " << value->GetBranchName() << '\n';
      return false;
   }
   return true;
}
// Analyze the tree "MyTree" in the file passed into the function.
// Returns false in case of errors.
bool analyze(TFile* file) {
   // Create a TTreeReader named "MyTree" from the given TDirectory.
   // The TTreeReader gives access to the TTree to the TTreeReaderValue and
   // TTreeReaderArray objects. It knows the current entry number and knows
   // how to iterate through the TTree.
   TTreeReader reader("MyTree", file);
   // Read a single float value in each tree entries:
   TTreeReaderValue<float> weight(reader, "event.weight");
   if (!CheckValue(weight)) return false;
   // Read a TriggerInfo object from the tree entries:
   TTreeReaderValue<TriggerInfo> triggerInfo(reader, "triggerInfo");
   if (!CheckValue(triggerInfo)) return false;
   //Read a vector of Muon objects from the tree entries:
   TTreeReaderValue<std::vector<Muon>> muons(reader, "muons");
   if (!CheckValue(muons)) return false;
   //Read the pT for all jets in the tree entry:
   TTreeReaderArray<double> jetPt(reader, "jets.pT");
   if (!CheckValue(jetPt)) return false;
   // Read the taus in the tree entry:
   TTreeReaderArray<Tau> taus(reader, "taus");
   if (!CheckValue(taus)) return false;
   // Now iterate through the TTree entries and fill a histogram.
   TH1F("hist", "TTreeReader example histogram", 10, 0., 100.);
   while (reader.Next()) {
      if (reader.GetEntryStatus() == kEntryValid) {
         std::cout << "Loaded entry " << reader.GetCurrentEntry() << '\n';
      } else {
         switch (reader.GetEntryStatus()) {
         kEntryValid:
            // Handled above.
            break;
         kEntryNotLoaded:
            std::cerr << "Error: TTreeReader has not loaded any data yet!\n";
            break;
         kEntryNoTree:
            std::cerr << "Error: TTreeReader cannot find a tree names \"MyTree\"!\n";
            break;
         kEntryNotFound:
            // Can't really happen as TTreeReader::Next() knows when to stop.
            std::cerr << "Error: The entry number doe not exist\n";
            break;
         kEntryChainSetupError:
            std::cerr << "Error: TTreeReader cannot access a chain element, e.g. file without the tree\n";
            break;
         kEntryChainFileError:
            std::cerr << "Error: TTreeReader cannot open a chain element, e.g. missing file\n";
            break;
         kEntryDictionaryError:
            std::cerr << "Error: TTreeReader cannot find the dictionary for some data\n";
            break;
         }
         return false;
      }
      // Access the TriggerInfo object as if it's a pointer.
      if (!triggerInfo->hasMuonL1())
         continue;
      // Ditto for the vector<Muon>.
      if (!muons->size())
         continue;
      // Access the jetPt as an array, whether the TTree stores this as
      // a std::vector, std::list, TClonesArray or Jet* C-style array, with
      // fixed or variable array size.
      if (jetPt.GetSize() < 2 || jetPt[0] < 100)
         continue;
      // Access the array of taus.
      if (!taus.IsEmpty()) {
         float currentWeight = *weight;
         for (int iTau = 0, nTau = taus.GetSize(); iTau < nTau; ++iTau) {
            // Access a float value - need to dereference as TTreeReaderValue
            // behaves like an iterator
            hist->Fill(taus[iTau].eta(), currentWeight);
         }
      }
   } // TTree entry / event loop
}

Definition at line 48 of file TTreeReader.h.

Classes
class	Iterator_t

Public Types
enum	EEntryStatus { kEntryValid = 0, kEntryNotLoaded, kEntryNoTree, kEntryNotFound, kEntryChainSetupError, kEntryChainFileError, kEntryDictionaryError, kEntryLast }

typedef Iterator_t	iterator

Public Types inherited from TObject
enum	EStatusBits { kCanDelete = BIT(0), kMustCleanup = BIT(3), kObjInCanvas = BIT(3), kIsReferenced = BIT(4), kHasUUID = BIT(5), kCannotPick = BIT(6), kNoContextMenu = BIT(8), kInvalidObject = BIT(13) }

enum	{ kIsOnHeap = 0x01000000, kNotDeleted = 0x02000000, kZombie = 0x04000000, kBitMask = 0x00ffffff }

enum	{ kSingleKey = BIT(0), kOverwrite = BIT(1), kWriteDelete = BIT(2) }

Public Member Functions
	TTreeReader ()

	TTreeReader (TTree *tree)

	TTreeReader (const char keyname, TDirectory dir=NULL)
	Access data from the tree called keyname in the directory (e.g. More...

	TTreeReader (const char , TFileCollection )

	~TTreeReader ()
	Tell all value readers that the tree reader does not exist anymore. More...

void	SetTree (TTree *tree)
	Set (or update) the which tree to reader from. More...

void	SetTree (const char , TDirectory )

void	SetChain (const char , TFileCollection )

Bool_t	IsChain () const

Bool_t	Next ()

EEntryStatus	SetEntry (Long64_t entry)

EEntryStatus	SetLocalEntry (Long64_t entry)

void	SetLastEntry (Long64_t entry)

EEntryStatus	SetEntriesRange (Long64_t first, Long64_t last)
	Set the range of entries to be processed. More...

EEntryStatus	GetEntryStatus () const

TTree *	GetTree () const

Long64_t	GetEntries (Bool_t force) const

Long64_t	GetCurrentEntry () const
	Returns the index of the current entry being read. More...

Iterator_t	begin ()

Iterator_t	end () const

Public Member Functions inherited from TObject
	TObject ()

	TObject (const TObject &object)
	TObject copy ctor. More...

TObject &	operator= (const TObject &rhs)
	TObject assignment operator. More...

virtual	~TObject ()
	TObject destructor. More...

virtual void	AppendPad (Option_t *option="")
	Append graphics object to current pad. More...

virtual void	Browse (TBrowser *b)
	Browse object. May be overridden for another default action. More...

virtual const char *	ClassName () const
	Returns name of class to which the object belongs. More...

virtual void	Clear (Option_t *="")

virtual TObject *	Clone (const char *newname="") const
	Make a clone of an object using the Streamer facility. More...

virtual Int_t	Compare (const TObject *obj) const
	Compare abstract method. More...

virtual void	Copy (TObject &object) const
	Copy this to obj. More...

virtual void	Delete (Option_t *option="")
	Delete this object. More...

virtual Int_t	DistancetoPrimitive (Int_t px, Int_t py)
	Computes distance from point (px,py) to the object. More...

virtual void	Draw (Option_t *option="")
	Default Draw method for all objects. More...

virtual void	DrawClass () const
	Draw class inheritance tree of the class to which this object belongs. More...

virtual TObject *	DrawClone (Option_t *option="") const
	Draw a clone of this object in the current pad. More...

virtual void	Dump () const
	Dump contents of object on stdout. More...

virtual void	Execute (const char method, const char params, Int_t *error=0)
	Execute method on this object with the given parameter string, e.g. More...

virtual void	Execute (TMethod method, TObjArray params, Int_t *error=0)
	Execute method on this object with parameters stored in the TObjArray. More...

virtual void	ExecuteEvent (Int_t event, Int_t px, Int_t py)
	Execute action corresponding to an event at (px,py). More...

virtual TObject *	FindObject (const char *name) const
	Must be redefined in derived classes. More...

virtual TObject *	FindObject (const TObject *obj) const
	Must be redefined in derived classes. More...

virtual Option_t *	GetDrawOption () const
	Get option used by the graphics system to draw this object. More...

virtual UInt_t	GetUniqueID () const
	Return the unique object id. More...

virtual const char *	GetName () const
	Returns name of object. More...

virtual const char *	GetIconName () const
	Returns mime type name of object. More...

virtual Option_t *	GetOption () const

virtual char *	GetObjectInfo (Int_t px, Int_t py) const
	Returns string containing info about the object at position (px,py). More...

virtual const char *	GetTitle () const
	Returns title of object. More...

virtual Bool_t	HandleTimer (TTimer *timer)
	Execute action in response of a timer timing out. More...

virtual ULong_t	Hash () const
	Return hash value for this object. More...

virtual Bool_t	InheritsFrom (const char *classname) const
	Returns kTRUE if object inherits from class "classname". More...

virtual Bool_t	InheritsFrom (const TClass *cl) const
	Returns kTRUE if object inherits from TClass cl. More...

virtual void	Inspect () const
	Dump contents of this object in a graphics canvas. More...

virtual Bool_t	IsFolder () const
	Returns kTRUE in case object contains browsable objects (like containers or lists of other objects). More...

virtual Bool_t	IsEqual (const TObject *obj) const
	Default equal comparison (objects are equal if they have the same address in memory). More...

virtual Bool_t	IsSortable () const

Bool_t	IsOnHeap () const

Bool_t	IsZombie () const

virtual Bool_t	Notify ()
	This method must be overridden to handle object notification. More...

virtual void	ls (Option_t *option="") const
	The ls function lists the contents of a class on stdout. More...

virtual void	Paint (Option_t *option="")
	This method must be overridden if a class wants to paint itself. More...

virtual void	Pop ()
	Pop on object drawn in a pad to the top of the display list. More...

virtual void	Print (Option_t *option="") const
	This method must be overridden when a class wants to print itself. More...

virtual Int_t	Read (const char *name)
	Read contents of object with specified name from the current directory. More...

virtual void	RecursiveRemove (TObject *obj)
	Recursively remove this object from a list. More...

virtual void	SaveAs (const char filename="", Option_t option="") const
	Save this object in the file specified by filename. More...

virtual void	SavePrimitive (std::ostream &out, Option_t *option="")
	Save a primitive as a C++ statement(s) on output stream "out". More...

virtual void	SetDrawOption (Option_t *option="")
	Set drawing option for object. More...

virtual void	SetUniqueID (UInt_t uid)
	Set the unique object id. More...

virtual void	UseCurrentStyle ()
	Set current style settings in this object This function is called when either TCanvas::UseCurrentStyle or TROOT::ForceStyle have been invoked. More...

virtual Int_t	Write (const char *name=0, Int_t option=0, Int_t bufsize=0)
	Write this object to the current directory. More...

virtual Int_t	Write (const char *name=0, Int_t option=0, Int_t bufsize=0) const
	Write this object to the current directory. More...

void *	operator new (size_t sz)

void *	operator new[] (size_t sz)

void *	operator new (size_t sz, void *vp)

void *	operator new[] (size_t sz, void *vp)

void	operator delete (void *ptr)
	Operator delete. More...

void	operator delete[] (void *ptr)
	Operator delete []. More...

void	SetBit (UInt_t f, Bool_t set)
	Set or unset the user status bits as specified in f. More...

void	SetBit (UInt_t f)

void	ResetBit (UInt_t f)

Bool_t	TestBit (UInt_t f) const

Int_t	TestBits (UInt_t f) const

void	InvertBit (UInt_t f)

virtual void	Info (const char method, const char msgfmt,...) const
	Issue info message. More...

virtual void	Warning (const char method, const char msgfmt,...) const
	Issue warning message. More...

virtual void	Error (const char method, const char msgfmt,...) const
	Issue error message. More...

virtual void	SysError (const char method, const char msgfmt,...) const
	Issue system error message. More...

virtual void	Fatal (const char method, const char msgfmt,...) const
	Issue fatal error message. More...

void	AbstractMethod (const char *method) const
	Use this method to implement an "abstract" method that you don't want to leave purely abstract. More...

void	MayNotUse (const char *method) const
	Use this method to signal that a method (defined in a base class) may not be called in a derived class (in principle against good design since a child class should not provide less functionality than its parent, however, sometimes it is necessary). More...

void	Obsolete (const char method, const char asOfVers, const char *removedFromVers) const
	Use this method to declare a method obsolete. More...

Protected Member Functions
void	Initialize ()
	Initialization of the director. More...

ROOT::Internal::TNamedBranchProxy *	FindProxy (const char *branchname) const

TCollection *	GetProxies ()

void	RegisterValueReader (ROOT::Internal::TTreeReaderValueBase *reader)
	Add a value reader for this tree. More...

void	DeregisterValueReader (ROOT::Internal::TTreeReaderValueBase *reader)
	Remove a value reader for this tree. More...

EEntryStatus	SetEntryBase (Long64_t entry, Bool_t local)
	Load an entry into the tree, return the status of the read. More...

Protected Member Functions inherited from TObject
void	MakeZombie ()

virtual void	DoError (int level, const char location, const char fmt, va_list va) const
	Interface to ErrorHandler (protected). More...

Private Types
enum	EPropertyBits { kBitIsChain = BIT(14) }

Private Member Functions
	ClassDef (TTreeReader, 0)

Private Attributes
TTree *	fTree

TDirectory *	fDirectory

EEntryStatus	fEntryStatus

ROOT::Internal::TBranchProxyDirector *	fDirector

std::deque < ROOT::Internal::TTreeReaderValueBase * >	fValues

THashTable	fProxies

Long64_t	fLastEntry

Bool_t	fProxiesSet

Friends
class	ROOT::Internal::TTreeReaderValueBase

class	ROOT::Internal::TTreeReaderArrayBase

Additional Inherited Members
Static Public Member Functions inherited from TObject
static Long_t	GetDtorOnly ()
	Return destructor only flag. More...

static void	SetDtorOnly (void *obj)
	Set destructor only flag. More...

static Bool_t	GetObjectStat ()
	Get status of object stat flag. More...

static void	SetObjectStat (Bool_t stat)
	Turn on/off tracking of objects in the TObjectTable. More...

#include <TTreeReader.h>

Inheritance diagram for TTreeReader:

[legend]

Member Typedef Documentation

typedef Iterator_t TTreeReader::iterator

Definition at line 126 of file TTreeReader.h.

Member Enumeration Documentation

enum TTreeReader::EEntryStatus

Enumerator
kEntryValid
kEntryNotLoaded
kEntryNoTree
kEntryNotFound
kEntryChainSetupError
kEntryChainFileError
kEntryDictionaryError
kEntryLast

Definition at line 128 of file TTreeReader.h.

enum TTreeReader::EPropertyBits

private

Enumerator
kBitIsChain

Definition at line 189 of file TTreeReader.h.

Constructor & Destructor Documentation

TTreeReader::TTreeReader ( )

inline

Definition at line 139 of file TTreeReader.h.

TTreeReader::TTreeReader ( TTree * tree )

TTreeReader::TTreeReader	(	const char *	keyname,
		TDirectory *	dir = `NULL`
	)

Access data from the tree called keyname in the directory (e.g.

TFile) dir, or the current directory if dir is NULL. If keyname cannot be found, or if it is not a TTree, IsZombie() will return true.

Definition at line 214 of file TTreeReader.cxx.

TTreeReader::TTreeReader	(	const char *	,
		TFileCollection *
	)

inline

Definition at line 148 of file TTreeReader.h.

TTreeReader::~TTreeReader ( )

Tell all value readers that the tree reader does not exist anymore.

Definition at line 230 of file TTreeReader.cxx.

Member Function Documentation

Iterator_t TTreeReader::begin ( )

inline

Definition at line 170 of file TTreeReader.h.

TTreeReader::ClassDef	(	TTreeReader	,
		0
	)

private

void TTreeReader::DeregisterValueReader ( ROOT::Internal::TTreeReaderValueBase * reader )

protected

Remove a value reader for this tree.

Definition at line 370 of file TTreeReader.cxx.

Referenced by ROOT::Internal::TTreeReaderValueBase::~TTreeReaderValueBase().

Iterator_t TTreeReader::end ( ) const

inline

Definition at line 174 of file TTreeReader.h.

ROOT::Internal::TNamedBranchProxy* TTreeReader::FindProxy ( const char * branchname ) const

inlineprotected

Definition at line 178 of file TTreeReader.h.

Long64_t TTreeReader::GetCurrentEntry ( ) const

Returns the index of the current entry being read.

Definition at line 272 of file TTreeReader.cxx.

Referenced by Next().

Long64_t TTreeReader::GetEntries ( Bool_t force ) const

inline

Definition at line 167 of file TTreeReader.h.

EEntryStatus TTreeReader::GetEntryStatus ( ) const

inline

Definition at line 164 of file TTreeReader.h.

TCollection* TTreeReader::GetProxies ( )

inlineprotected

Definition at line 180 of file TTreeReader.h.

TTree* TTreeReader::GetTree ( ) const

inline

Definition at line 166 of file TTreeReader.h.

Referenced by h1analysisTreeReader::Notify().

void TTreeReader::Initialize ( )

protected

Initialization of the director.

Definition at line 243 of file TTreeReader.cxx.

Referenced by SetTree(), and TTreeReader().

Bool_t TTreeReader::IsChain ( ) const

inline

Definition at line 156 of file TTreeReader.h.

Bool_t TTreeReader::Next ( )

inline

Definition at line 158 of file TTreeReader.h.

void TTreeReader::RegisterValueReader ( ROOT::Internal::TTreeReaderValueBase * reader )

protected

Add a value reader for this tree.

Definition at line 362 of file TTreeReader.cxx.

void TTreeReader::SetChain	(	const char *	,
		TFileCollection *
	)

inline

Definition at line 154 of file TTreeReader.h.

TTreeReader::EEntryStatus TTreeReader::SetEntriesRange	(	Long64_t	first,
		Long64_t	last
	)

Set the range of entries to be processed.

If last > first, this call is equivalent to SetEntry(first); SetLastEntry(last);. Otherwise last is ignored and only first is set.

Returns: the EEntryStatus that would be returned by SetEntry(first)

Definition at line 260 of file TTreeReader.cxx.

Referenced by TPoolProcessor< F >::Process().

EEntryStatus TTreeReader::SetEntry ( Long64_t entry )

inline

Definition at line 159 of file TTreeReader.h.

Referenced by Next(), and TTreeReader::Iterator_t::operator*().

TTreeReader::EEntryStatus TTreeReader::SetEntryBase	(	Long64_t	entry,
		Bool_t	local
	)

protected

Load an entry into the tree, return the status of the read.

For chains, entry is the global (i.e. not tree-local) entry number.

Definition at line 285 of file TTreeReader.cxx.

Referenced by SetEntry(), and SetLocalEntry().

void TTreeReader::SetLastEntry ( Long64_t entry )

inline

Definition at line 161 of file TTreeReader.h.

EEntryStatus TTreeReader::SetLocalEntry ( Long64_t entry )

inline

Definition at line 160 of file TTreeReader.h.

Referenced by h1analysisTreeReader::Process(), and SetEntriesRange().

void TTreeReader::SetTree ( TTree * tree )

Set (or update) the which tree to reader from.

tree can be a TTree or a TChain.

Definition at line 340 of file TTreeReader.cxx.

Referenced by h1analysisTreeReader::Init().

void TTreeReader::SetTree	(	const char *	,
		TDirectory *
	)

inline

Definition at line 153 of file TTreeReader.h.

Friends And Related Function Documentation

friend class ROOT::Internal::TTreeReaderArrayBase

friend

Definition at line 203 of file TTreeReader.h.

friend class ROOT::Internal::TTreeReaderValueBase

friend

Definition at line 202 of file TTreeReader.h.

Member Data Documentation

ROOT::Internal::TBranchProxyDirector* TTreeReader::fDirector

private

Definition at line 196 of file TTreeReader.h.

Referenced by GetCurrentEntry(), Initialize(), SetEntryBase(), SetTree(), and ~TTreeReader().

TDirectory* TTreeReader::fDirectory

private

Definition at line 194 of file TTreeReader.h.

Referenced by TTreeReader().

EEntryStatus TTreeReader::fEntryStatus

private

Definition at line 195 of file TTreeReader.h.

Referenced by GetEntryStatus(), Initialize(), and SetEntryBase().

Long64_t TTreeReader::fLastEntry

private

Definition at line 199 of file TTreeReader.h.

Referenced by SetEntriesRange(), SetEntryBase(), and SetLastEntry().

THashTable TTreeReader::fProxies

private

Definition at line 198 of file TTreeReader.h.

Referenced by FindProxy(), GetProxies(), and ~TTreeReader().

Bool_t TTreeReader::fProxiesSet

private

Definition at line 200 of file TTreeReader.h.

Referenced by SetEntryBase().

TTree* TTreeReader::fTree

private

Definition at line 193 of file TTreeReader.h.

Referenced by GetCurrentEntry(), GetEntries(), GetTree(), Initialize(), SetEntryBase(), SetTree(), and TTreeReader().

std::deque<ROOT::Internal::TTreeReaderValueBase*> TTreeReader::fValues

private

Definition at line 197 of file TTreeReader.h.

Referenced by DeregisterValueReader(), RegisterValueReader(), SetEntryBase(), and ~TTreeReader().

Collaboration diagram for TTreeReader:

[legend]

The documentation for this class was generated from the following files:

tree/treeplayer/inc/TTreeReader.h
tree/treeplayer/src/TTreeReader.cxx

Classes

Public Types

Public Member Functions

Protected Member Functions

Private Types

Private Member Functions

Private Attributes

Friends

Additional Inherited Members

Member Typedef Documentation

Member Enumeration Documentation

Constructor & Destructor Documentation

Member Function Documentation

Friends And Related Function Documentation

Member Data Documentation