doc/v606/rebin_8C.html

#include "TH1.h"

#include "TCanvas.h"

void rebin() {

   //create a fix bin histogram

   TH1F *h = new TH1F("h","test rebin",100,-3,3);

   Int_t nentries = 1000;

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

   Double_t xbins[1001];

   Int_t k=0;

   TAxis *axis = h->GetXaxis();

   for (Int_t i=1;i<=100;i++) {

      Int_t y = (Int_t)h->GetBinContent(i);

      if (y <=0) continue;

      Double_t dx = axis->GetBinWidth(i)/y;

      Double_t xmin = axis->GetBinLowEdge(i);

      for (Int_t j=0;j<y;j++) {

         xbins[k] = xmin +j*dx;

         k++;

      }

   }

   xbins[k] = axis->GetXmax();

   //create a variable bin-width histogram out of fix bin histogram

   //new rebinned histogram should have about 10 entries per bin

   TH1F *hnew = new TH1F("hnew","rebinned",k,xbins);

   hnew->FillRandom("gaus",10*nentries);


   //rebin hnew keeping only 50% of the bins

   Double_t xbins2[501];

   Int_t kk=0;

   for (Int_t j=0;j<k;j+=2) {

      xbins2[kk] = xbins[j];

      kk++;

   }

   xbins2[kk] = xbins[k];

   TH1F *hnew2 = (TH1F*)hnew->Rebin(kk,"hnew2",xbins2);


   //draw the 3 histograms

   TCanvas *c1 = new TCanvas("c1","c1",800,1000);

   c1->Divide(1,3);

   c1->cd(1);

   h->Draw();

   c1->cd(2);

   hnew->Draw();

   c1->cd(3);

   hnew2->Draw();

}