From $ROOTSYS/tutorials/graphs/labels1.C

//Setting alphanumeric labels in a 1-d histogram
//Author; Rene Brun
void labels1()
{
   Int_t i;
   const Int_t nx = 20;
   const char *people[nx] = {"Jean","Pierre","Marie","Odile",
      "Sebastien","Fons","Rene","Nicolas","Xavier","Greg",
      "Bjarne","Anton","Otto","Eddy","Peter","Pasha",
      "Philippe","Suzanne","Jeff","Valery"};
   TCanvas *c1 = new TCanvas("c1","demo bin labels",10,10,900,500);
   c1->SetGrid();
   c1->SetBottomMargin(0.15);
   TH1F *h = new TH1F("h","test",nx,0,nx);
   h->SetFillColor(38);
   for (i=0;i<5000;i++) h->Fill(gRandom->Gaus(0.5*nx,0.2*nx));
   h->SetStats(0);
   for (i=1;i<=nx;i++) h->GetXaxis()->SetBinLabel(i,people[i-1]);
   h->Draw();
   TPaveText *pt = new TPaveText(0.6,0.7,0.98,0.98,"brNDC");
   pt->SetFillColor(18);
   pt->SetTextAlign(12);
   pt->AddText("Use the axis Context Menu LabelsOption");
   pt->AddText(" \"a\"   to sort by alphabetic order");
   pt->AddText(" \">\"   to sort by decreasing values");
   pt->AddText(" \"<\"   to sort by increasing values");
   pt->Draw();
}
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