Save THStack in root file

[BethLong06]

Feature description

I would like to be able to save an identical object to what’s produced interactively when making a stack plot, ie with this MWE:

void TRatioPlotStack()
{
  
  gStyle->SetHistLineColor(kBlack);
  gStyle->SetMarkerStyle(8);
  gStyle->SetMarkerSize(0.7);
  TGaxis::SetMaxDigits(3);
  gROOT->ForceStyle();
  gStyle->SetOptStat(0);
  
  auto C = new TCanvas("C", "A ratio example");

  auto h1 = new TH1D("h1", "TRatioPlot Example; x; y", 50, 0, 10);
  auto h2 = new TH1D("h2", "h2", 50, 0, 10);
  auto h3 = new TH1D("h3", "h3", 50, 0, 10);

  auto f1 = new TF1("f1", "exp(- x/[0] )");
  f1->SetParameter(0, 3);

  for(int ii=0; ii<h1->GetXaxis()->GetNbins(); ii++) h1->SetBinContent(ii+1,150);
  
  h2->FillRandom("f1", 2000);
  h3->FillRandom("f1", 2000);

  h1->Sumw2();
  h1->SetOption("E");
  
  h2->Scale(1. / 2.);
  h2->SetFillColor(kRed);
  h3->SetFillColor(kBlue);

  THStack* st = new THStack("st","");
  st->Add(h2);
  st->Add(h3);

  auto rp = new TRatioPlot(h1, st);
  C->SetTicks(0, 1);
  rp->Draw();
  rp->GetLowYaxis()->SetNdivisions(505);

  TFile* fFile = TFile::Open("~/Desktop/test.root","recreate");
  //  fFile->cd();
  rp->Write();
  fFile->Close();
}

to save this:

Currently I get this: Where even clicking on h1/h2 doesn’t show anything

Alternatives considered

No response

Additional context

No response

[ferdymercury]

As workaround, you could call C->Write() which saves everything on the canvas.

Then, double clicking would work. To retrieve the objects, just:

C->ls();
C->FindObject("TRatioPlot")

[linev]

Yes, store of TCanvas is the only working way to store TRatioPlot object

[dpiparo]

I think what could lead to confusion is the fact that TRatioPlot, as the name suggests, is a helper to draw ratios, and not an object thought to be persistified.

[couet]

Indeed, it does not really make sense to save a TRatioPlot, as it is not a self-contained object like a TH1 or a TGraph. TRatioPlot is a class designed to lay out pads, and you can clearly see this if you inspect the pad contents (via gPad->ls()): several pads and axes are generated.

In addition, TRatioPlot is not a named class and therefore cannot be accessed via ratioplot->Draw() from the command line. As mentioned before, you should save the entire canvas or use another method to save it (PDF, SVG, PNG, etc.).

We will improve the TRatioPlot doc.