Looping over a TTree

evcount.cxx

// Find the number of events simulated and the efficiency for a set of ntuples
// Usage: root -b -q "evcount.cxx([filename], rate=0)"  # "filename" can have wildcards
// If provided, rate is events/detector-year
void evcount(TString filenames, float rate=0) {
  TChain tc("output");
  tc.Add(filenames);
  int entries = tc.GetEntries();
  cout << "Total entries: " << entries << endl;

  // ROOT branch pointers
  int evIndex;
  tc.SetBranchAddress("evIndex", &evIndex);
  bool scintFit;
  tc.SetBranchAddress("scintFit", &scintFit);

  // Counters
  int mc_events = 0;
  int triggered = 0;
  int reconstructed = 0;

  for (int i=0; i<entries; i++) {
    if (i % 10000 == 0) {
      cout << ".";
      cout.flush();
    }

    tc.GetEntry(i);

    if (evIndex == -1 || evIndex == 0) {
      mc_events++;
    }

    if (evIndex == 0) {
      triggered++;
      if (scintFit) {
        reconstructed++;
      }
    }
  }

  cout << endl << "Simulated: " << mc_events;
  if (rate > 0) {
    cout << " (" << 1.0 * mc_events / rate << " years)";
  }
  cout << endl;
  cout << "Triggered: " << triggered << " (" << 1.0 * triggered / mc_events << ")" << endl;
  cout << "Recon'ed:  " << reconstructed << " (" << 1.0 * reconstructed / triggered << ")" << endl;
}