TH2 *t12d(TList *alist, const char *name2d=0) {
   //convert 1d histograms in list to a 2d histogram
   // Histograms in list  are converted to a 2d histogram . 
   // The 2d histogram is named names2d if name2d is not null 

   if (!alist) return 0;
   Int_t nh = alist->GetSize();
   if (!nh) return 0;
   TH1 *h1 = (TH1*)alist->At(0);
   TAxis *axis = h1->GetXaxis();
   Int_t nbins = axis->GetNbins();
   TH2F *h2 = new TH2F(name2d,h1->GetTitle(),nbins,
      axis->GetXmin(),axis->GetXmax(), nh,0,nh);
   Int_t biny = 0;
   Double_t nentries = 0;
   TIter next(alist);
   while ((h1 = (TH1*)next())) {
      biny++;
      nentries += h1->GetEntries();
      for (Int_t i=0;i<nbins;i++) {
         h2->SetBinContent(i,biny,h1->GetBinContent(i));
      }
   }
   h2->SetEntries(nentries);
   h2->SetDirectory(0);
   return h2;
}
         
   
TH2 *t12d(const char *names, const char *name2d=0) {
   //convert 1d histograms to a 2d histogram
   //if names = 0, all 1-d histograms in the current directory on disk
   //              are converted to a 2d
   // if names = xxx all 1d histograms with a name starting with "xxx"
   // are converted to a 2d histogram . The 2d histogram is named names2d
   // if name2d is not null and xxx2d otherwise.
   
   TList *alist = new TList();
   TIter next(gDirectory->GetListOfKeys());
   TKey *key;
   while ((key = (TKey*)next())) {
      if (!names && !strstr(key->GetClassName(),"TH1")) continue;
      if (names && strstr(key->GetName(),names) != key->GetName()) continue;
      TObject *obj = key->ReadObj();
      if (!obj->InheritsFrom("TH1")) continue;
      alist->Add(obj);
   }
   TH2 *h2 = t12d(alist,"h2d");
   alist->Delete();
   delete alist;
   return h2;
}
TH2 *t12d() {
   TFile f("All_chiSig-histos.root");
   TH2 *h2 = t12d("hrAPD");
   h2->Draw("box");
   return h2;
}