TSelector

Class Description

                                                                        
 A TSelector object is used by the TTree::Draw, TTree::Scan,            
 TTree::Loop, TTree::Process to navigate in a TTree and make            
 selections. It contains the following main methods:                    
                                                                        
 void TSelector::Init(TTree *t). Called every time a new TTree is       
    attached.                                                           
 void TSelector::Begin(). This method is called before looping on the   
    events in the Tree. The user can create his histograms in this      
    function. When using PROOF Begin() is called on the client only.    
    Histogram creation should preferable be done in SlaveBegin() in     
    that case.                                                          
 void TSelector::SlaveBegin(). This method is called on each PROOF      
    worker node. The user can create his histograms in this method.     
    In local mode this method is called on the client too.              
                                                                        
 Bool_t TSelector::Notify(). This method is called at the first entry   
    of a new file in a chain.                                           
                                                                        
 Bool_t TSelector::Process(Long64_t entry). This method is called       
    to process an event. It is the user's responsability to read        
    the corresponding entry in memory (may be just a partial read).     
    Once the entry is in memory one can apply a selection and if the    
    event is selected histograms can be filled. Processing stops        
    when this function returns kFALSE. This function combines the       
    next two functions in one, avoiding to have to maintain state       
    in the class to communicate between these two funtions.             
    See WARNING below about entry.                                      
    This method is used by PROOF.                                       
 Bool_t TSelector::ProcessCut(Long64_t entry). This method is called    
    before processing entry. It is the user's responsability to read    
    the corresponding entry in memory (may be just a partial read).     
    The function returns kTRUE if the entry must be processed,          
    kFALSE otherwise. This method is obsolete, use Process().           
    See WARNING below about entry.                                      
 void TSelector::ProcessFill(Long64_t entry). This method is called     
    for all selected events. User fills histograms in this function.    
    This method is obsolete, use Process().                             
    See WARNING below about entry.                                      
 void TSelector::SlaveTerminate(). This method is called at the end of  
    the loop on all PROOF worker nodes. In local mode this method is    
    called on the client too.                                           
 void TSelector::Terminate(). This method is called at the end of       
    the loop on all events. When using PROOF Terminate() is call on     
    the client only. Typically one performs the fits on the produced    
    histograms or write the histograms to file in this method.          
                                                                        
 WARNING when a selector is used with a TChain:                         
    in the Process, ProcessCut, ProcessFill function, you must use      
    the pointer to the current Tree to call GetEntry(entry).            
    entry is always the local entry number in the current tree.         
    Assuming that fChain is the pointer to the TChain being processed,  
    use fChain->GetTree()->GetEntry(entry);