void rebins() {
// example of script to rebin a 1-d histogram grouping:
//   2 bins together upto 50
//   5 bins together upto 80
//  10 bins together upto 100
   
   TF1 f1("f1","0.1/x",0,100);
   TH1F *h1 = new TH1F("h1","original histo",100,0,100);
   h1->FillRandom("f1",3000);
 
   Int_t bin = 1;
   Double_t bins[80];
   Int_t nbins = 0;
   TAxis *xaxis = h1->GetXaxis();
   while (bin <100) {
      bins[nbins] = xaxis->GetBinLowEdge(bin);
      nbins++;
      if (bin < 50)      bin += 2;
      else if (bin < 80) bin += 5;
      else               bin += 10;
   }             
   bins[nbins] = xaxis->GetBinUpEdge(100);
   
   TH1F *h2 = new TH1F("h2","rebinned histo",nbins,bins);
   for (bin=1;bin<100;bin++) {
      h2->Fill(xaxis->GetBinCenter(bin),h1->GetBinContent(bin));
   }
   TCanvas *c1 = new TCanvas("c1","c1",600,800);
   c1->Divide(1,2);
   c1->cd(1);
   h1->Draw();
   c1->cd(2);
   h2->Draw();
}