// compile with g++ $(root-config --cflags) -o RooHistPdf_and_derived_variables_1 RooHistPdf_and_derived_variables_1.cc $(root-config --libs) -lRooFitCore -lRooFit

#include "RooAddPdf.h"
#include "RooDataSet.h"
#include "RooExponential.h"
#include "RooGaussian.h"
#include "RooPlot.h"
#include "RooFormulaVar.h"
#include "RooDataHist.h"
#include "RooHistPdf.h"
#include "RooPolyVar.h"
#include "RooRealSumPdf.h"
#include "RooRealVar.h"
#include "RooBinning.h"
#include "TH1D.h"
#include "TCanvas.h"

int main(int argc, char const *argv[]) {

    // Elementary variables with event weight
    RooRealVar px("px","px",10,0,100);
    RooRealVar py("py","py",10,0,100);

    RooRealVar weight("weight","weight",10,0,100);

    // Create RooDataSet for unbinned data
    RooDataSet ds("ds", "ds", RooArgSet(px, py, weight), "weight");

    // Fill the data set
    int n_vals = 3;
    std::vector<double> px_vals{2.0, 7.0, 11.0};
    std::vector<double> py_vals{4.58257569495584, 13.2664991614216, 22.44994432064365};
    std::vector<double> weight_vals{3, 1, 0.1};
    for(int i = 0; i < n_vals; ++i) {
        px.setVal(px_vals[i]);
        py.setVal(py_vals[i]);
        ds.add(RooArgSet(px, py), weight_vals[i]);
    }

    // Derived variables
    RooFormulaVar pt_func("pt","sqrt(px**2 + py**2)", RooArgList(px,py));

    // This is the important line to get the derived variable in the data set
    auto pt = (RooRealVar*) ds.addColumn(pt_func) ;

    // Set the binning
    RooBinning pt_bins(10,0,100);
    pt->setBinning(pt_bins);

    // Get some into
    pt->Print();
    ds.Print();

    // Check the values and binning
    TCanvas canvas("canvas", "canvas", 500, 500);
    ds.createHistogram("pt")->Draw();
    canvas.SaveAs("canvas.png");

    // This does now work.
    RooDataHist rdh("rdh","rdh", *pt, ds);

    // Make a RooHistPdf
    RooHistPdf pdf("pdf", "pdf", *pt, rdh);

  return 0;
}