rf102_dataimport.C

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/// \file
/// \ingroup tutorial_roofit
/// \notebook -js
/// Basic functionality: importing data from ROOT TTrees and THx histograms
///
/// \macro_image
/// \macro_output
/// \macro_code
/// \author 07/2008 - Wouter Verkerke

#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooDataHist.h"
#include "RooGaussian.h"
#include "TCanvas.h"
#include "RooPlot.h"
#include "TTree.h"
#include "TH1D.h"
#include "TRandom.h"
using namespace RooFit;

TH1 *makeTH1();
TTree *makeTTree();

void rf102_dataimport()
{
   // ---------------------------------------------------
   // I m p o r t i n g   R O O T   h i s t o g r a m s
   // ===================================================

   // I m p o r t   T H 1   i n t o   a   R o o D a t a H i s t
   // ---------------------------------------------------------

   // Create a ROOT TH1 histogram
   TH1 *hh = makeTH1();

   // Declare observable x
   RooRealVar x("x", "x", -10, 10);

   // Create a binned dataset that imports contents of TH1 and associates its contents to observable 'x'
   RooDataHist dh("dh", "dh", x, Import(*hh));

   // P l o t   a n d   f i t   a   R o o D a t a H i s t
   // ---------------------------------------------------

   // Make plot of binned dataset showing Poisson error bars (RooFit default)
   RooPlot *frame = x.frame(Title("Imported TH1 with Poisson error bars"));
   dh.plotOn(frame);

   // Fit a Gaussian p.d.f to the data
   RooRealVar mean("mean", "mean", 0, -10, 10);
   RooRealVar sigma("sigma", "sigma", 3, 0.1, 10);
   RooGaussian gauss("gauss", "gauss", x, mean, sigma);
   gauss.fitTo(dh);
   gauss.plotOn(frame);

   // P l o t   a n d   f i t   a   R o o D a t a H i s t   w i t h   i n t e r n a l   e r r o r s
   // ---------------------------------------------------------------------------------------------

   // If histogram has custom error (i.e. its contents is does not originate from a Poisson process
   // but e.g. is a sum of weighted events) you can data with symmetric 'sum-of-weights' error instead
   // (same error bars as shown by ROOT)
   RooPlot *frame2 = x.frame(Title("Imported TH1 with internal errors"));
   dh.plotOn(frame2, DataError(RooAbsData::SumW2));
   gauss.plotOn(frame2);

   // Please note that error bars shown (Poisson or SumW2) are for visualization only, the are NOT used
   // in a maximum likelihood fit
   //
   // A (binned) ML fit will ALWAYS assume the Poisson error interpretation of data (the mathematical definition
   // of likelihood does not take any external definition of errors). Data with non-unit weights can only be correctly
   // fitted with a chi^2 fit (see rf602_chi2fit.C)

   // -----------------------------------------
   // I m p o r t i n g   R O O T  T T r e e s
   // =========================================

   // I m p o r t   T T r e e   i n t o   a   R o o D a t a S e t
   // -----------------------------------------------------------

   TTree *tree = makeTTree();

   // Define 2nd observable y
   RooRealVar y("y", "y", -10, 10);

   // Construct unbinned dataset importing tree branches x and y matching between branches and RooRealVars
   // is done by name of the branch/RRV
   //
   // Note that ONLY entries for which x,y have values within their allowed ranges as defined in
   // RooRealVar x and y are imported. Since the y values in the import tree are in the range [-15,15]
   // and RRV y defines a range [-10,10] this means that the RooDataSet below will have less entries than the TTree
   // 'tree'

   RooDataSet ds("ds", "ds", RooArgSet(x, y), Import(*tree));

   // U s e   a s c i i   i m p o r t / e x p o r t   f o r   d a t a s e t s
   // ------------------------------------------------------------------------------------
   {
      // Write data to output stream
      std::ofstream outstream("rf102_testData.txt");
      // Optionally, adjust the stream here (e.g. std::setprecision)
      ds.write(outstream);
      outstream.close();
   }

   // Read data from input stream. The variables of the dataset need to be supplied
   // to the RooDataSet::read() function.
   std::cout << "\n-----------------------\nReading data from ASCII\n";
   RooDataSet *dataReadBack =
      RooDataSet::read("rf102_testData.txt",
                       RooArgList(x, y), // variables to be read. If the file has more fields, these are ignored.
                       "D"); // Prints if a RooFit message stream listens for debug messages. Use Q for quiet.

   dataReadBack->Print("V");

   std::cout << "\nOriginal data, line 20:\n";
   ds.get(20)->Print("V");

   std::cout << "\nRead-back data, line 20:\n";
   dataReadBack->get(20)->Print("V");

   // P l o t   d a t a s e t s  w i t h   m u l t i p l e   b i n n i n g   c h o i c e s
   // ------------------------------------------------------------------------------------

   // Print number of events in dataset
   ds.Print();

   // Print unbinned dataset with default frame binning (100 bins)
   RooPlot *frame3 = y.frame(Title("Unbinned data shown in default frame binning"));
   ds.plotOn(frame3);

   // Print unbinned dataset with custom binning choice (20 bins)
   RooPlot *frame4 = y.frame(Title("Unbinned data shown with custom binning"));
   ds.plotOn(frame4, Binning(20));

   RooPlot *frame5 = y.frame(Title("Unbinned data read back from ASCII file"));
   ds.plotOn(frame5, Binning(20));
   dataReadBack->plotOn(frame5, Binning(20), MarkerColor(kRed), MarkerStyle(5));

   // Draw all frames on a canvas
   TCanvas *c = new TCanvas("rf102_dataimport", "rf102_dataimport", 1000, 800);
   c->Divide(3, 2);
   c->cd(1);
   gPad->SetLeftMargin(0.15);
   frame->GetYaxis()->SetTitleOffset(1.4);
   frame->Draw();
   c->cd(2);
   gPad->SetLeftMargin(0.15);
   frame2->GetYaxis()->SetTitleOffset(1.4);
   frame2->Draw();

   c->cd(4);
   gPad->SetLeftMargin(0.15);
   frame3->GetYaxis()->SetTitleOffset(1.4);
   frame3->Draw();
   c->cd(5);
   gPad->SetLeftMargin(0.15);
   frame4->GetYaxis()->SetTitleOffset(1.4);
   frame4->Draw();
   c->cd(6);
   gPad->SetLeftMargin(0.15);
   frame4->GetYaxis()->SetTitleOffset(1.4);
   frame5->Draw();
}

TH1 *makeTH1()
{
   // Create ROOT TH1 filled with a Gaussian distribution

   TH1D *hh = new TH1D("hh", "hh", 25, -10, 10);
   for (int i = 0; i < 100; i++) {
      hh->Fill(gRandom->Gaus(0, 3));
   }
   return hh;
}

TTree *makeTTree()
{
   // Create ROOT TTree filled with a Gaussian distribution in x and a uniform distribution in y

   TTree *tree = new TTree("tree", "tree");
   Double_t *px = new Double_t;
   Double_t *py = new Double_t;
   tree->Branch("x", px, "x/D");
   tree->Branch("y", py, "y/D");
   for (int i = 0; i < 100; i++) {
      *px = gRandom->Gaus(0, 3);
      *py = gRandom->Uniform() * 30 - 15;
      tree->Fill();
   }
   return tree;
}