root-6.10.00/html/quantiles_8C.html

void quantiles() {

   const Int_t nq = 100;

   const Int_t nshots = 10;

   Double_t xq[nq];  // position where to compute the quantiles in [0,1]

   Double_t yq[nq];  // array to contain the quantiles

   for (Int_t i=0;i<nq;i++) xq[i] = Float_t(i+1)/nq;


   TGraph *gr70 = new TGraph(nshots);

   TGraph *gr90 = new TGraph(nshots);

   TGraph *gr98 = new TGraph(nshots);

   TH1F *h = new TH1F("h","demo quantiles",50,-3,3);


   for (Int_t shot=0;shot<nshots;shot++) {

      h->FillRandom("gaus",50);

      h->GetQuantiles(nq,yq,xq);

      gr70->SetPoint(shot,shot+1,yq[70]);

      gr90->SetPoint(shot,shot+1,yq[90]);

      gr98->SetPoint(shot,shot+1,yq[98]);

   }


   //show the original histogram in the top pad

   TCanvas *c1 = new TCanvas("c1","demo quantiles",10,10,600,900);

   c1->Divide(1,3);

   c1->cd(1);

   h->SetFillColor(38);

   h->Draw();


   // show the final quantiles in the middle pad

   c1->cd(2);

   gPad->SetGrid();

   TGraph *gr = new TGraph(nq,xq,yq);

   gr->SetTitle("final quantiles");

   gr->SetMarkerStyle(21);

   gr->SetMarkerColor(kRed);

   gr->SetMarkerSize(0.3);

   gr->Draw("ap");


   // show the evolution of some  quantiles in the bottom pad

   c1->cd(3);

   gPad->DrawFrame(0,0,nshots+1,3.2);

   gPad->SetGrid();

   gr98->SetMarkerStyle(22);

   gr98->SetMarkerColor(kRed);

   gr98->Draw("lp");

   gr90->SetMarkerStyle(21);

   gr90->SetMarkerColor(kBlue);

   gr90->Draw("lp");

   gr70->SetMarkerStyle(20);

   gr70->SetMarkerColor(kMagenta);

   gr70->Draw("lp");

   // add a legend

   TLegend *legend = new TLegend(0.85,0.74,0.95,0.95);

   legend->SetTextFont(72);

   legend->SetTextSize(0.05);

   legend->AddEntry(gr98," q98","lp");

   legend->AddEntry(gr90," q90","lp");

   legend->AddEntry(gr70," q70","lp");

   legend->Draw();

}