#include<iostream>
#include<fstream>
#include<TFile.h>
#include<TNtuple.h>
#include<TCanvas.h>
#include<TH2F.h>

void dat_root()
  { 
   ifstream data;
   Float_t xF, pT, xsect, error;
   
   data.open("data.txt");
   TFile* file = new TFile("data.root","RECREATE");
   
  // TTree* tree = 0;
   
   TNtuple* ntup = new TNtuple("ntup","import data file","xF:pT:xsect:error");
   
   while(1){ 
   data>>xF>>pT>>xsect>>error;
   if(!data.good()) break;
   
   ntup->Fill(xF,pT,xsect,error);
  // cout<<xF<<pT<<xsect<<error<<endl;
   }
   
   data.close();
   file->Write();
  
   
   file->Get("ntup");
   
   //access branch 
   
   ntup->SetBranchAddress("xF",&xF);
   ntup->SetBranchAddress("pT",&pT);
   ntup->SetBranchAddress("xsect",&xsect);
   ntup->SetBranchAddress("error",&error);
   
    Int_t nEntries = 271;
    Int_t nbins = 270;   
   
   TH2F* hist = new TH2F(""," ",nbins,0,0.5,nbins,0,1);
   TH1F* hist_c = new TH1F(""," ",nbins,0,700);//,nbins,0,1);
   TCanvas* c = new TCanvas("c","",800,600); 
    
    
   for (Int_t i = 0; i<nEntries; i++)
     { 
       ntup->GetEntry(i);
       hist->Fill(xF,pT);
      // hist_c->Fill(xsect,error); 
       //hist_c->Fill(xsect,error);    
     }
     
   hist->SetMarkerStyle(kFullDotMedium);
   hist->SetMarkerColor(1);
  
   hist->GetXaxis()->SetRangeUser(0,0.5);
   hist->GetYaxis()->SetRangeUser(0,1); 
   //ntup->Draw("xF:pT","xsect","COLZ");
  // hist->SetCellError(xF,pT,error);
   hist->Draw("COLZ");  
   hist->SetLineColor(kBlack);
   //ntup->Draw("pT:xF","error","colz"); // for weighting with error
 //  hist_c->Draw("COLZ SAME");   
   hist->GetXaxis()->SetTitle("Feynman Variable  xF");
   hist->GetYaxis()->SetTitle("Momentum Transverse pT");
   c->Update();
}