using FourVector = ROOT::Math::XYZTVector;
using FourVectorVec = std::vector<FourVector>;
using FourVectorRVec = ROOT::VecOps::RVec<FourVector>;
using CylFourVector = ROOT::Math::RhoEtaPhiVector;
// A simple helper function to fill a test tree: this makes the example
// stand-alone.
void fill_tree(const char *filename, const char *treeName)
{
   const double M = 0.13957; // set pi+ mass
   TRandom3 R(1);
   auto genTracks = [&](){
      FourVectorVec tracks;
      const auto nPart = R.Poisson(15);
      tracks.reserve(nPart);
      for (int j = 0; j < nPart; ++j) {
         const auto px = R.Gaus(0, 10);
         const auto py = R.Gaus(0, 10);
         const auto pt = sqrt(px * px + py * py);
         const auto eta = R.Uniform(-3, 3);
         const auto phi = R.Uniform(0.0, 2 * TMath::Pi());
         CylFourVector vcyl(pt, eta, phi);
         // set energy
         auto E = sqrt(vcyl.R() * vcyl.R() + M * M);
         // fill track vector
         tracks.emplace_back(vcyl.X(), vcyl.Y(), vcyl.Z(), E);
      }
      return tracks;
   };
   ROOT::RDataFrame d(64);
   d.Define("tracks", genTracks).Snapshot<FourVectorVec>(treeName, filename, {"tracks"});
}

void test(){
    auto fileName = "df002_dataModel.root";
    auto treeName = "myTree";
    fill_tree(fileName, treeName);

    ROOT::RDataFrame df(treeName, fileName, {"tracks"});
    auto d = df.Filter([](ULong64_t e){if (0ULL == e) std::cout << "Running evtloop" << std::endl; return true;},{"rdfentry_"});
    //d.Snapshot("myNewTree", "newfile.root");
    // now start to work on 'd'. At every loop, at he first event, you'll have a message.
    auto h1 = df.Histo1D("tracks_pts");
    h1->Draw();
}