A simple, robust and fast interface to read values from ROOT columnar datasets such as TTree, TChain or TNtuple.

TTreeReader is associated to TTreeReaderValue and TTreeReaderArray which are handles to concretely access the information in the dataset.

Example code can be found in

You can generate a skeleton of TTreeReaderValue<T> and TTreeReaderArray<T> declarations for all of a tree's branches using TTree::MakeSelector().

Roottest contains an example showing the full power.

A simpler analysis example 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::Internal::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");
 
   // Read a TriggerInfo object from the tree entries:
   TTreeReaderValue<TriggerInfo> triggerInfo(reader, "triggerInfo");
 
   //Read a vector of Muon objects from the tree entries:
   TTreeReaderValue<std::vector<Muon>> muons(reader, "muons");
 
   //Read the pT for all jets in the tree entry:
   TTreeReaderArray<double> jetPt(reader, "jets.pT");
 
   // Read the taus in the tree entry:
   TTreeReaderArray<Tau> taus(reader, "taus");
 
 
   // Now iterate through the TTree entries and fill a histogram.
 
   TH1F("hist", "TTreeReader example histogram", 10, 0., 100.);
 
   bool firstEntry = true;
   while (reader.Next()) {
      if (firstEntry) {
         // Check that branches exist and their types match our expectation.
         if (!CheckValue(weight)) return false;
         if (!CheckValue(triggerInfo)) return false;
         if (!CheckValue(muons)) return false;
         if (!CheckValue(jetPt)) return false;
         if (!CheckValue(taus)) return false;
         firstentry = 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()) {
         // Access a float value - need to dereference as TTreeReaderValue
         // behaves like an iterator
         float currentWeight = *weight;
         for (const Tau& tau: taus) {
            hist->Fill(tau.eta(), currentWeight);
         }
      }
   } // TTree entry / event loop
 
   // Return true if we have iterated through all entries.
   return reader.GetEntryStatus() == TTreeReader::kEntryBeyondEnd;
}

Definition at line 44 of file TTreeReader.h.

Classes
class	Iterator_t
	Iterate through the entries of a TTree. More...

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

enum	ELoadTreeStatus { kNoTree = 0 , kLoadTreeNone , kInternalLoadTree , kExternalLoadTree }

typedef Iterator_t	iterator

Public Types inherited from TObject
enum	{ kIsOnHeap = 0x01000000 , kNotDeleted = 0x02000000 , kZombie = 0x04000000 , kInconsistent = 0x08000000 , kBitMask = 0x00ffffff }

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

enum	EDeprecatedStatusBits { kObjInCanvas = (1ULL << ( 3 )) }

enum	EStatusBits { kCanDelete = (1ULL << ( 0 )) , kMustCleanup = (1ULL << ( 3 )) , kIsReferenced = (1ULL << ( 4 )) , kHasUUID = (1ULL << ( 5 )) , kCannotPick = (1ULL << ( 6 )) , kNoContextMenu = (1ULL << ( 8 )) , kInvalidObject = (1ULL << ( 13 )) }

Public Member Functions
	TTreeReader ()
	Default constructor. Call SetTree to connect to a TTree.

	TTreeReader (const char keyname, TDirectory dir, TEntryList *entryList=nullptr)
	Access data from the tree called keyname in the directory (e.g.

	TTreeReader (const char keyname, TEntryList entryList=nullptr)

	TTreeReader (TTree tree, TEntryList entryList=nullptr)
	Access data from tree.

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

Iterator_t	begin ()
	Return an iterator to the 0th TTree entry.

Iterator_t	end ()
	Return an iterator beyond the last TTree entry.

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

Long64_t	GetEntries () const
	Returns the number of entries of the TEntryList if one is provided, else of the TTree / TChain, independent of a range set by SetEntriesRange() by calling TTree/TChain::GetEntriesFast.

Long64_t	GetEntries (bool force)
	Returns the number of entries of the TEntryList if one is provided, else of the TTree / TChain, independent of a range set by SetEntriesRange().

TEntryList *	GetEntryList () const

EEntryStatus	GetEntryStatus () const

TTree *	GetTree () const

TClass *	IsA () const override

bool	IsChain () const

bool	IsInvalid () const

bool	Notify () override
	Notify director and values of a change in tree.

void	SetTree (const char keyname, TDirectory dir, TEntryList *entryList=nullptr)
	Set (or update) the which tree to read from, passing the name of a tree in a directory.

void	SetTree (const char keyname, TEntryList entryList=nullptr)

void	SetTree (TTree tree, TEntryList entryList=nullptr)
	Set (or update) the which tree to read from.

void	Streamer (TBuffer &) override
	Stream an object of class TObject.

void	StreamerNVirtual (TBuffer &ClassDef_StreamerNVirtual_b)

Entry setters
bool	Next ()
	Move to the next entry (or index of the TEntryList if that is set).

EEntryStatus	SetEntry (Long64_t entry)
	Set the next entry (or index of the TEntryList if that is set).

EEntryStatus	SetLocalEntry (Long64_t entry)
	Set the next local tree entry.

EEntryStatus	SetEntriesRange (Long64_t beginEntry, Long64_t endEntry)
	Set the range of entries to be loaded by `Next()`; end will not be loaded.

std::pair< Long64_t, Long64_t >	GetEntriesRange () const
	Get the begin and end entry numbers.

void	Restart ()
	Restart a Next() loop from entry 0 (of TEntryList index 0 of fEntryList is set).

Public Member Functions inherited from TObject
	TObject ()
	TObject constructor.

	TObject (const TObject &object)
	TObject copy ctor.

virtual	~TObject ()
	TObject destructor.

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

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

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

ULong_t	CheckedHash ()
	Check and record whether this class has a consistent Hash/RecursiveRemove setup (*) and then return the regular Hash value for this object.

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

virtual void	Clear (Option_t *="")

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

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

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

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

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

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

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

virtual TObject *	DrawClone (Option_t *option="") const
	Draw a clone of this object in the current selected pad with: `gROOT->SetSelectedPad(c1)`.

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

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

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

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

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

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

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

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

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

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

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

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

virtual Option_t *	GetOption () const

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

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

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

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

Bool_t	HasInconsistentHash () const
	Return true is the type of this object is known to have an inconsistent setup for Hash and RecursiveRemove (i.e.

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

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

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

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

void	InvertBit (UInt_t f)

Bool_t	IsDestructed () const
	IsDestructed.

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

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

R__ALWAYS_INLINE Bool_t	IsOnHeap () const

virtual Bool_t	IsSortable () const

R__ALWAYS_INLINE Bool_t	IsZombie () const

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

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).

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

void	operator delete (void *ptr)
	Operator delete.

void	operator delete (void ptr, void vp)
	Only called by placement new when throwing an exception.

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

void	operator delete[] (void ptr, void vp)
	Only called by placement new[] when throwing an exception.

void *	operator new (size_t sz)

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

void *	operator new[] (size_t sz)

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

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

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

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

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

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

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

void	ResetBit (UInt_t f)

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

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

void	SetBit (UInt_t f)

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

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

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

void	StreamerNVirtual (TBuffer &ClassDef_StreamerNVirtual_b)

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

R__ALWAYS_INLINE Bool_t	TestBit (UInt_t f) const

Int_t	TestBits (UInt_t f) const

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

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

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

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

Static Public Member Functions
static TClass *	Class ()

static const char *	Class_Name ()

static constexpr Version_t	Class_Version ()

static const char *	DeclFileName ()

Static Public Member Functions inherited from TObject
static TClass *	Class ()

static const char *	Class_Name ()

static constexpr Version_t	Class_Version ()

static const char *	DeclFileName ()

static Longptr_t	GetDtorOnly ()
	Return destructor only flag.

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

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

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

Static Public Attributes
static constexpr const char *const	fgEntryStatusText [kEntryUnknownError+1]

Protected Types
using	NamedProxies_t = std::unordered_map< std::string, std::unique_ptr< ROOT::Internal::TNamedBranchProxy > >

Protected Types inherited from TObject
enum	{ kOnlyPrepStep = (1ULL << ( 3 )) }

Protected Member Functions
void	AddProxy (ROOT::Internal::TNamedBranchProxy *p)

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

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

void	Initialize ()
	Initialization of the director.

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

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

bool	SetProxies ()
	Tell readers we now have a tree.

Protected Member Functions inherited from TObject
virtual void	DoError (int level, const char location, const char fmt, va_list va) const
	Interface to ErrorHandler (protected).

void	MakeZombie ()

Private Types
enum	EStatusBits { kBitIsChain = (1ULL << ( 14 )) , kBitHaveWarnedAboutEntryListAttachedToTTree = (1ULL << ( 15 )) , kBitSetEntryBaseCallingLoadTree = (1ULL << ( 16 )) }

Private Member Functions
std::string	GetProxyKey (const char *branchname)

Private Attributes
Long64_t	fBeginEntry = 0LL
	This allows us to propagate the range to the TTreeCache.

ROOT::Internal::TBranchProxyDirector *	fDirector = nullptr
	proxying director, owned

Long64_t	fEndEntry = -1LL
	The end of the entry loop.

Long64_t	fEntry = -1
	Current (non-local) entry of fTree or of fEntryList if set.

TEntryList *	fEntryList = nullptr
	entry list to be used

EEntryStatus	fEntryStatus = kEntryNotLoaded
	status of most recent read request

std::deque< ROOT::Internal::TFriendProxy * >	fFriendProxies
	proxying for friend TTrees, owned

ELoadTreeStatus	fLoadTreeStatus = kNoTree
	Indicator on how LoadTree was called 'last' time.

TNotifyLink< TTreeReader >	fNotify
	TTree and TChain will notify this object upon LoadTree, leading to a call to TTreeReader::Notify().

NamedProxies_t	fProxies
	attached ROOT::TNamedBranchProxies; owned

bool	fProxiesSet = false
	True if the proxies have been set, false otherwise.

bool	fSetEntryBaseCallingLoadTree = false
	True if during the LoadTree execution triggered by SetEntryBase.

TTree *	fTree = nullptr
	tree that's read

std::deque< ROOT::Internal::TTreeReaderValueBase * >	fValues
	readers that use our director

Friends
class	ROOT::Internal::TTreeReaderArrayBase

class	ROOT::Internal::TTreeReaderValueBase

#include <TTreeReader.h>

Inheritance diagram for TTreeReader:

[legend]

Member Typedef Documentation

◆ iterator

typedef Iterator_t TTreeReader::iterator

Definition at line 148 of file TTreeReader.h.

◆ NamedProxies_t

using TTreeReader::NamedProxies_t = std::unordered_map<std::string, std::unique_ptr<ROOT::Internal::TNamedBranchProxy> >

protected

Definition at line 266 of file TTreeReader.h.

Member Enumeration Documentation

◆ EEntryStatus

enum TTreeReader::EEntryStatus

Enumerator
kEntryValid	data read okay
kEntryNotLoaded	no entry has been loaded yet
kEntryNoTree	the tree does not exist
kEntryNotFound	the tree entry number does not exist
kEntryChainSetupError	problem in accessing a chain element, e.g. file without the tree
kEntryChainFileError	problem in opening a chain's file
kEntryDictionaryError	problem reading dictionary info from tree
kEntryBeyondEnd	last entry loop has reached its end
kEntryBadReader	One of the readers was not successfully initialized.
kEntryUnknownError	LoadTree return less than -4, likely a 'newer' error code.

Definition at line 150 of file TTreeReader.h.

◆ ELoadTreeStatus

enum TTreeReader::ELoadTreeStatus

Enumerator
kNoTree	default state, no TTree is connected (formerly 'Zombie' state)
kLoadTreeNone	Notify has not been called yet.
kInternalLoadTree	Notify/LoadTree was last called from SetEntryBase.
kExternalLoadTree	User code called LoadTree directly.

Definition at line 163 of file TTreeReader.h.

◆ EStatusBits

enum TTreeReader::EStatusBits

private

Enumerator
kBitIsChain	our tree is a chain
kBitHaveWarnedAboutEntryListAttachedToTTree	the tree had a TEntryList and we have warned about that
kBitSetEntryBaseCallingLoadTree	SetEntryBase is in the process of calling TChain/TTree::LoadTree.

Definition at line 303 of file TTreeReader.h.

Constructor & Destructor Documentation

◆ TTreeReader() [1/4]

TTreeReader::TTreeReader ( )

Default constructor. Call SetTree to connect to a TTree.

Definition at line 190 of file TTreeReader.cxx.

◆ TTreeReader() [2/4]

TTreeReader::TTreeReader	(	TTree *	tree,
		TEntryList *	entryList = `nullptr`
	)

Access data from tree.

Parameters

tree	The TTree or TChain to read from
entryList	It can be a single TEntryList with global entry numbers (supported, as an extension, also in the case of a TChain) or, if the first parameter is a TChain, a TEntryList with sub-TEntryLists with local entry numbers. In the latter case, the TEntryList must be associated to the TChain, as per chain.SetEntryList(&entryList).

Definition at line 202 of file TTreeReader.cxx.

◆ TTreeReader() [3/4]

TTreeReader::TTreeReader	(	const char *	keyname,
		TDirectory *	dir,
		TEntryList *	entryList = `nullptr`
	)

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, IsInvalid() will return true.

Parameters

keyname	The name of the TTree to read from file
dir	The TDirectory to read keyname from
entryList	It can be a single TEntryList with global entry numbers (supported, as an extension, also in the case of a TChain) or, if the first parameter is a TChain, a TEntryList with sub-TEntryLists with local entry numbers. In the latter case, the TEntryList must be associated to the TChain, as per chain.SetEntryList(&entryList).

Definition at line 227 of file TTreeReader.cxx.

◆ TTreeReader() [4/4]

TTreeReader::TTreeReader	(	const char *	keyname,
		TEntryList *	entryList = `nullptr`
	)

inline

Definition at line 186 of file TTreeReader.h.

◆ ~TTreeReader()

TTreeReader::~TTreeReader ( )

override

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

Definition at line 245 of file TTreeReader.cxx.

Member Function Documentation

◆ AddProxy()

void TTreeReader::AddProxy ( ROOT::Internal::TNamedBranchProxy * p )

inlineprotected

Definition at line 274 of file TTreeReader.h.

◆ begin()

Iterator_t TTreeReader::begin ( )

inline

Return an iterator to the 0th TTree entry.

Definition at line 259 of file TTreeReader.h.

◆ Class()

static TClass * TTreeReader::Class ( )

static

Returns: TClass describing this class

◆ Class_Name()

static const char * TTreeReader::Class_Name ( )

static

Returns: Name of this class

◆ Class_Version()

static constexpr Version_t TTreeReader::Class_Version ( )

inlinestaticconstexpr

Returns: Version of this class

Definition at line 333 of file TTreeReader.h.

◆ DeclFileName()

static const char * TTreeReader::DeclFileName ( )

inlinestatic

Returns: Name of the file containing the class declaration

Definition at line 333 of file TTreeReader.h.

◆ DeregisterValueReader()

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

protected

Remove a value reader for this tree.

Definition at line 687 of file TTreeReader.cxx.

◆ end()

Iterator_t TTreeReader::end ( )

inline

Return an iterator beyond the last TTree entry.

Definition at line 263 of file TTreeReader.h.

◆ FindProxy()

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

inlineprotected

Definition at line 268 of file TTreeReader.h.

◆ GetCurrentEntry()

Long64_t TTreeReader::GetCurrentEntry ( ) const

inline

Returns the index of the current entry being read.

If IsChain(), the returned index corresponds to the global entry number (i.e. not the entry number local to the chain's current tree). If fEntryList, the returned index corresponds to an index in the TEntryList; to translate to the TChain's / TTree's entry number pass it through reader.GetEntryList()->GetEntry(reader.GetCurrentEntry()).

Definition at line 254 of file TTreeReader.h.

◆ GetEntries() [1/2]

Long64_t TTreeReader::GetEntries ( ) const

Returns the number of entries of the TEntryList if one is provided, else of the TTree / TChain, independent of a range set by SetEntriesRange() by calling TTree/TChain::GetEntriesFast.

Definition at line 468 of file TTreeReader.cxx.

◆ GetEntries() [2/2]

Long64_t TTreeReader::GetEntries ( bool force )

Returns the number of entries of the TEntryList if one is provided, else of the TTree / TChain, independent of a range set by SetEntriesRange().

Parameters

force If IsChain() and force, determines whether all TFiles of this TChain should be opened to determine the exact number of entries of the TChain. If !IsChain(), force is ignored.

Definition at line 485 of file TTreeReader.cxx.

◆ GetEntriesRange()

std::pair< Long64_t, Long64_t > TTreeReader::GetEntriesRange ( ) const

inline

Get the begin and end entry numbers.

Returns: a pair contained the begin and end entry numbers.

Definition at line 235 of file TTreeReader.h.

◆ GetEntryList()

TEntryList * TTreeReader::GetEntryList ( ) const

inline

Definition at line 201 of file TTreeReader.h.

◆ GetEntryStatus()

EEntryStatus TTreeReader::GetEntryStatus ( ) const

inline

Definition at line 242 of file TTreeReader.h.

◆ GetProxyKey()

std::string TTreeReader::GetProxyKey ( const char * branchname )

inlineprivate

Definition at line 296 of file TTreeReader.h.

◆ GetTree()

TTree * TTreeReader::GetTree ( ) const

inline

Definition at line 200 of file TTreeReader.h.

◆ Initialize()

void TTreeReader::Initialize ( )

protected

Initialization of the director.

Definition at line 269 of file TTreeReader.cxx.

◆ IsA()

TClass * TTreeReader::IsA ( ) const

inlineoverridevirtual

Returns: TClass describing current object

Reimplemented from TObject.

Definition at line 333 of file TTreeReader.h.

◆ IsChain()

bool TTreeReader::IsChain ( ) const

inline

Definition at line 196 of file TTreeReader.h.

◆ IsInvalid()

bool TTreeReader::IsInvalid ( ) const

inline

Definition at line 198 of file TTreeReader.h.

◆ Next()

bool TTreeReader::Next ( )

inline

Move to the next entry (or index of the TEntryList if that is set).

Returns: false if the previous entry was already the last entry. This allows the function to be used in while (reader.Next()) { ... }

Definition at line 209 of file TTreeReader.h.

◆ Notify()

bool TTreeReader::Notify ( )

overridevirtual

Notify director and values of a change in tree.

Called from TChain and TTree's LoadTree. TTreeReader registers its fNotify data member with the TChain/TTree which in turn leads to this method being called upon the execution of LoadTree.

Reimplemented from TObject.

Definition at line 307 of file TTreeReader.cxx.

◆ RegisterValueReader()

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

protected

Add a value reader for this tree.

Definition at line 672 of file TTreeReader.cxx.

◆ Restart()

void TTreeReader::Restart ( )

Restart a Next() loop from entry 0 (of TEntryList index 0 of fEntryList is set).

Definition at line 450 of file TTreeReader.cxx.

◆ SetEntriesRange()

TTreeReader::EEntryStatus TTreeReader::SetEntriesRange	(	Long64_t	beginEntry,
		Long64_t	endEntry
	)

Set the range of entries to be loaded by Next(); end will not be loaded.

If end <= begin, end is ignored (set to -1, i.e. will run on all entries from begin onwards).

Example:

reader.SetEntriesRange(3, 5);
while (reader.Next()) {
  // Will load entries 3 and 4.
}

Note that if a TEntryList is present, beginEntry and endEntry refer to the beginEntry-th/endEntry-th entries of the TEntryList (or the main TEntryList in case it has sub-entrylists). In other words, SetEntriesRange can be used to only loop over part of the TEntryList, but not to further restrict the actual TTree/TChain entry numbers considered.

Parameters

beginEntry	The first entry to be loaded by `Next()`.
endEntry	The entry where `Next()` will return false, not loading it.

Definition at line 412 of file TTreeReader.cxx.

◆ SetEntry()

EEntryStatus TTreeReader::SetEntry ( Long64_t entry )

inline

Set the next entry (or index of the TEntryList if that is set).

Parameters

entry If not TEntryList is set, the entry is a global entry (i.e. not the entry number local to the chain's current tree).

Returns: the entry's read status, i.e. whether the entry is available.

Definition at line 218 of file TTreeReader.h.

◆ SetEntryBase()

TTreeReader::EEntryStatus TTreeReader::SetEntryBase	(	Long64_t	entry,
		bool	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, unless local is true, in which case entry specifies the entry number within the current tree. This is needed for instance for TSelector::Process().

Definition at line 509 of file TTreeReader.cxx.

◆ SetLocalEntry()

EEntryStatus TTreeReader::SetLocalEntry ( Long64_t entry )

inline

Set the next local tree entry.

If a TEntryList is set, this function is equivalent to SetEntry().

Parameters

entry Entry number of the TChain's current TTree. This is the entry number passed for instance by TSelector::Process(entry), i.e. within TSelector::Process() always use SetLocalEntry() and not SetEntry()!

Returns: the entry's read status, i.e. whether the entry is available.

Definition at line 228 of file TTreeReader.h.

◆ SetProxies()

bool TTreeReader::SetProxies ( )

protected

Tell readers we now have a tree.

fValues gets insertions during this loop (when parametrized arrays are read), invalidating iterators. Use old-school counting instead.

Definition at line 353 of file TTreeReader.cxx.

◆ SetTree() [1/3]

void TTreeReader::SetTree	(	const char *	keyname,
		TDirectory *	dir,
		TEntryList *	entryList = `nullptr`
	)

Set (or update) the which tree to read from, passing the name of a tree in a directory.

Parameters

keyname	- name of the tree in `dir`
dir	- the `TDirectory` to load `keyname` from (or gDirectory if `nullptr`)
entryList	- the `TEntryList` to attach to the `TTreeReader`.

Definition at line 660 of file TTreeReader.cxx.

◆ SetTree() [2/3]

void TTreeReader::SetTree	(	const char *	keyname,
		TEntryList *	entryList = `nullptr`
	)

inline

Definition at line 191 of file TTreeReader.h.

◆ SetTree() [3/3]

void TTreeReader::SetTree	(	TTree *	tree,
		TEntryList *	entryList = `nullptr`
	)

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

tree can be a TTree or a TChain.

Definition at line 630 of file TTreeReader.cxx.

◆ Streamer()

void TTreeReader::Streamer ( TBuffer & R__b )

overridevirtual

Stream an object of class TObject.

Reimplemented from TObject.

◆ StreamerNVirtual()

void TTreeReader::StreamerNVirtual ( TBuffer & ClassDef_StreamerNVirtual_b )

inline

Definition at line 333 of file TTreeReader.h.

Friends And Related Symbol Documentation

◆ ROOT::Internal::TTreeReaderArrayBase

friend class ROOT::Internal::TTreeReaderArrayBase

friend

Definition at line 331 of file TTreeReader.h.

◆ ROOT::Internal::TTreeReaderValueBase

friend class ROOT::Internal::TTreeReaderValueBase

friend

Definition at line 330 of file TTreeReader.h.

Member Data Documentation

◆ fBeginEntry

Long64_t TTreeReader::fBeginEntry = 0LL

private

This allows us to propagate the range to the TTreeCache.

Definition at line 326 of file TTreeReader.h.

◆ fDirector

ROOT::Internal::TBranchProxyDirector* TTreeReader::fDirector = nullptr

private

proxying director, owned

Definition at line 315 of file TTreeReader.h.

◆ fEndEntry

Long64_t TTreeReader::fEndEntry = -1LL

private

The end of the entry loop.

When set (i.e. >= 0), it provides a way to stop looping over the TTree when we reach a certain entry: Next() returns false when GetCurrentEntry() reaches fEndEntry.

Definition at line 325 of file TTreeReader.h.

◆ fEntry

Long64_t TTreeReader::fEntry = -1

private

Current (non-local) entry of fTree or of fEntryList if set.

Definition at line 320 of file TTreeReader.h.

◆ fEntryList

TEntryList* TTreeReader::fEntryList = nullptr

private

entry list to be used

Definition at line 310 of file TTreeReader.h.

◆ fEntryStatus

EEntryStatus TTreeReader::fEntryStatus = kEntryNotLoaded

private

status of most recent read request

Definition at line 311 of file TTreeReader.h.

◆ fFriendProxies

std::deque<ROOT::Internal::TFriendProxy*> TTreeReader::fFriendProxies

private

proxying for friend TTrees, owned

Definition at line 316 of file TTreeReader.h.

◆ fgEntryStatusText

constexpr const char *const TTreeReader::fgEntryStatusText

staticconstexpr

Initial value:

= {
      "valid entry",
      "the tree does not exist",
      "the tree entry number does not exist",
      "cannot access chain element",
      "problem in opening a chain's file",
      "problem reading dictionary info from tree",
      "last entry loop has reached its end",
      "one of the readers was not successfully initialized",
      "LoadTree return less than -4, likely a 'newer' error code"
   }

Definition at line 170 of file TTreeReader.h.

◆ fLoadTreeStatus

ELoadTreeStatus TTreeReader::fLoadTreeStatus = kNoTree

private

Indicator on how LoadTree was called 'last' time.

Definition at line 312 of file TTreeReader.h.

◆ fNotify

TNotifyLink<TTreeReader> TTreeReader::fNotify

private

TTree and TChain will notify this object upon LoadTree, leading to a call to TTreeReader::Notify().

Definition at line 314 of file TTreeReader.h.

◆ fProxies

NamedProxies_t TTreeReader::fProxies

private

attached ROOT::TNamedBranchProxies; owned

Definition at line 318 of file TTreeReader.h.

◆ fProxiesSet

bool TTreeReader::fProxiesSet = false

private

True if the proxies have been set, false otherwise.

Definition at line 327 of file TTreeReader.h.

◆ fSetEntryBaseCallingLoadTree

bool TTreeReader::fSetEntryBaseCallingLoadTree = false

private

True if during the LoadTree execution triggered by SetEntryBase.

Definition at line 328 of file TTreeReader.h.

◆ fTree

TTree* TTreeReader::fTree = nullptr

private

tree that's read

Definition at line 309 of file TTreeReader.h.

◆ fValues

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

private

readers that use our director

Definition at line 317 of file TTreeReader.h.

Libraries 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

Static Public Member Functions

Static Public Attributes

Protected Types

Protected Member Functions

Private Types

Private Member Functions

Private Attributes

Friends

Member Typedef Documentation

◆ iterator

◆ NamedProxies_t

Member Enumeration Documentation

◆ EEntryStatus

◆ ELoadTreeStatus

◆ EStatusBits

Constructor & Destructor Documentation

◆ TTreeReader() [1/4]

◆ TTreeReader() [2/4]

◆ TTreeReader() [3/4]

◆ TTreeReader() [4/4]

◆ ~TTreeReader()

Member Function Documentation

◆ AddProxy()

◆ begin()

◆ Class()

◆ Class_Name()

◆ Class_Version()

◆ DeclFileName()

◆ DeregisterValueReader()

◆ end()

◆ FindProxy()

◆ GetCurrentEntry()

◆ GetEntries() [1/2]

◆ GetEntries() [2/2]

◆ GetEntriesRange()

◆ GetEntryList()

◆ GetEntryStatus()

◆ GetProxyKey()

◆ GetTree()

◆ Initialize()

◆ IsA()

◆ IsChain()

◆ IsInvalid()

◆ Next()

◆ Notify()

◆ RegisterValueReader()

◆ Restart()

◆ SetEntriesRange()

◆ SetEntry()

◆ SetEntryBase()

◆ SetLocalEntry()

◆ SetProxies()

◆ SetTree() [1/3]

◆ SetTree() [2/3]

◆ SetTree() [3/3]

◆ Streamer()

◆ StreamerNVirtual()

Friends And Related Symbol Documentation

◆ ROOT::Internal::TTreeReaderArrayBase

◆ ROOT::Internal::TTreeReaderValueBase

Member Data Documentation

◆ fBeginEntry

◆ fDirector

◆ fEndEntry

◆ fEntry

◆ fEntryList

◆ fEntryStatus

◆ fFriendProxies

◆ fgEntryStatusText

◆ fLoadTreeStatus

◆ fNotify

◆ fProxies

◆ fProxiesSet

◆ fSetEntryBaseCallingLoadTree

◆ fTree

◆ fValues