#!/usr/bin/env python
# coding: utf-8

# # Access a TTree with the TTreeReader

# In[1]:


from ROOTaaS.iPyROOT import ROOT
ROOT.toCpp()


# Open a file which is located on the web. 
# Build a TTreeReader and two TTreeReader values, one for the tracks and one for the event number.

# In[2]:


auto f = TFile::Open("https://indico.cern.ch/event/395198/material/0/0.root");

TTreeReader myReader("events",f);
TTreeReaderValue<vector<ROOT::Math::PxPyPzEVector>> tracksRV(myReader, "tracks");
TTreeReaderValue<int> eventNumRV(myReader, "evtNum");


# Loop over the events stored in the tree. Analyse the transverse momentum of tracks and identify the maximum one.
# Print the result every one hundred events.

# In[3]:


double maxPt;
while(myReader.Next()){
   auto evtNum (*eventNumRV);

   auto tracks = *tracksRV;
   maxPt = -1;
   for (auto&& track : tracks){
      auto pt = track.Pt();
      if (pt>maxPt) maxPt = pt;
   }
   if (evtNum %100 == 0) {
      std::cout << "Processing event number " << evtNum << std::endl;
      std::cout << "Max pt is " << maxPt << std::endl;
   }

} 


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