#include <ROOT/RDataFrame.hxx>
#include <TTree.h>
#include <TFile.h>
#include <TChain.h>
#include <iostream>
#include <ROOT/TTreeProcessorMT.hxx>

void makeTree(int numEntries){
  TTree *tree = new TTree("tree","tree");
  double x = 2.0;
  tree->Branch("BeamEnergy",&x);
  for (int i = 0; i < numEntries; i++){
    tree->Fill();
  }
  TFile file("tree.root","recreate");
  file.cd();
  tree->Write();
}

void skimTree(){
  TChain* tree = new TChain("tree");
  tree->Add("tree.root");
  TFile file2("treeCopy.root","recreate");
  file2.cd();
  TTree* tree2 = tree->CopyTree("(1==1)");
  tree2->Write();
}

TH1F* dataframeMethod(TString fileName){
  ROOT::EnableImplicitMT(0);
  ROOT::RDataFrame DF("tree",fileName.Data());
  auto hDF = DF.Filter("(1==1)")
               .Define("VAR","BeamEnergy")
               .Histo1D({"NAME","TITLE",100,0.0,5.0},"VAR");
  TH1F hist; hDF->Copy(hist);
  return new TH1F(hist);
}

int main() {
   makeTree(1);
   skimTree();
   auto *h = dataframeMethod("treeCopy.root");
   std::cout << h->GetEntries() << std::endl;
   std::cout << h->GetMean() << std::endl;

	return 0;
}