Simple Macro to count the Number of Candidates

TH1* nCand( KanEventSource& input, const char* listName, UInt_t nEvt = 0) {
  // This is a simple macro to fill a 1D the # of candidate on a given list
  // The input is a KanEventSource.
  // The return value is the filled histogram
  //
  // To Build a KanEventSource you need to do:
  // root[0] KanEventSource* input = KanEventSource::mini("in");
  // root[1] input->Add("/A/Collection/Name")
  //
  // To invoke this macro you could do (for example)
  // root[2] .L ../KanExample/nCand.C
  // root[3] TH1F* hist = nCand(*input,"ChargedTracks");
  // root[4] hist->Draw();
  //
  // Note that this macro is the equivalent of doing:
  // root[5] input->getComponent(3)->Draw("Cnd_<list>__n");
  //
  

  // Setup the input data 
  TString theName("Cnd_");
  theName += listName;

  BtaCandHandleList cands(KanCompMap::cnd,theName.Data());
  input.setBranchToRead(cands);

  // Build the output histogram
  TH1F* hist = new TH1F("nCand","A plot of number of candidates on a list",31,-0.5,30.5);
  
  // Setup the Event Loop
  UInt_t n = (UInt_t)input.GetEntries();
  if ( nEvt > 0 ) {
    n = n > nEvt ? nEvt : n;
  }
  cout << "Will run on " << n << " events." << endl;
  
  // Event Loop
  for ( UInt_t i(0); i < n; ++i ) {

    // Load the event
    input.LoadTree(i);
    
    // Read the data
    if ( !cands(input) ) {
      cerr << "Failed to read branch object for event " << i << endl;
      break;
    }
    
    // Fill the output histogram
    hist->Fill((Float_t)(cands.size()));
  }
  
  // Return the histogram
  return hist;
}