ntpl008_import.C

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/// \file
/// \ingroup tutorial_ntuple
/// \notebook
/// Example of converting data stored in a TTree into an RNTuple
///
/// \macro_image
/// \macro_code
///
/// \date December 2022
/// \author The ROOT Team
 
// NOTE: The RNTuple classes are experimental at this point.
// Functionality, interface, and data format is still subject to changes.
// Do not use for real data!
 
// Until C++ runtime modules are universally used, we explicitly load the ntuple library.  Otherwise
// triggering autoloading from the use of templated types would require an exhaustive enumeration
// of "all" template instances in the LinkDef file.
R__LOAD_LIBRARY(ROOTNTupleUtil)
 
#include <ROOT/RNTuple.hxx>
#include <ROOT/RNTupleDS.hxx>
#include <ROOT/RNTupleImporter.hxx>
 
#include <TFile.h>
#include <TROOT.h>
 
// Import classes from experimental namespace for the time being.
using RNTuple = ROOT::Experimental::RNTuple;
using RNTupleImporter = ROOT::Experimental::RNTupleImporter;
using RNTupleReader = ROOT::Experimental::RNTupleReader;
 
// Input and output.
constexpr char const *kTreeFileName = "http://root.cern.ch/files/HiggsTauTauReduced/GluGluToHToTauTau.root";
constexpr char const *kTreeName = "Events";
constexpr char const *kNTupleFileName = "ntpl008_import.root";
 
void ntpl008_import()
{
   // RNTupleImporter appends keys to the output file; make sure a second run of the tutorial does not fail
   // with `Key 'Events' already exists in file ntpl008_import.root` by removing the output file.
   gSystem->Unlink(kNTupleFileName);
 
   // Use multiple threads to compress RNTuple data.
   ROOT::EnableImplicitMT();
 
   // Create a new RNTupleImporter object.
   auto importer = RNTupleImporter::Create(kTreeFileName, kTreeName, kNTupleFileName);
 
   // Begin importing.
   importer->Import();
 
   // Inspect the schema of the written RNTuple.
   auto file = std::unique_ptr<TFile>(TFile::Open(kNTupleFileName));
   if (!file || file->IsZombie()) {
      std::cerr << "cannot open " << kNTupleFileName << std::endl;
      return;
   }
   auto ntpl = file->Get<RNTuple>("Events");
   auto reader = RNTupleReader::Open(ntpl);
   reader->PrintInfo();
 
   auto df = ROOT::RDF::Experimental::FromRNTuple("Events", kNTupleFileName);
   df.Histo1D({"Jet_pt", "Jet_pt", 100, 0, 0}, "Jet_pt")->DrawCopy();
}