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TTreeReader Class Reference

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 "TriggerInfo.h"
#include "Muon.h"
#include "Tau.h"
#include <vector>
#include <iostream>
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()) {
// Handled above.
break;
std::cerr << "Error: TTreeReader has not loaded any data yet!\n";
break;
std::cerr << "Error: TTreeReader cannot find a tree names \"MyTree\"!\n";
break;
// Can't really happen as TTreeReader::Next() knows when to stop.
std::cerr << "Error: The entry number doe not exist\n";
break;
std::cerr << "Error: TTreeReader cannot access a chain element, e.g. file without the tree\n";
break;
std::cerr << "Error: TTreeReader cannot open a chain element, e.g. missing file\n";
break;
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
 
TTreeGetTree () 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...
 
TObjectoperator= (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 TObjectClone (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 TObjectDrawClone (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 TObjectFindObject (const char *name) const
 Must be redefined in derived classes. More...
 
virtual TObjectFindObject (const TObject *obj) const
 Must be redefined in derived classes. More...
 
virtual Option_tGetDrawOption () 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_tGetOption () 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...
 
voidoperator new (size_t sz)
 
voidoperator new[] (size_t sz)
 
voidoperator new (size_t sz, void *vp)
 
voidoperator 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::TNamedBranchProxyFindProxy (const char *branchname) const
 
TCollectionGetProxies ()
 
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

TTreefTree
 
TDirectoryfDirectory
 
EEntryStatus fEntryStatus
 
ROOT::Internal::TBranchProxyDirectorfDirector
 
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

Definition at line 126 of file TTreeReader.h.

Member Enumeration Documentation

Enumerator
kEntryValid 
kEntryNotLoaded 
kEntryNoTree 
kEntryNotFound 
kEntryChainSetupError 
kEntryChainFileError 
kEntryDictionaryError 
kEntryLast 

Definition at line 128 of file TTreeReader.h.

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  ,
 
)
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

Definition at line 203 of file TTreeReader.h.

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
std::deque<ROOT::Internal::TTreeReaderValueBase*> TTreeReader::fValues
private
Collaboration diagram for TTreeReader:
[legend]

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