Histogram is empty when writing it to a new root file

[naikal_mc]

Hello all,

I am trying to copy a histogram from file X.root to Y.root since I do not want to deal with directories in python. However, when I open the histogram written to file Y.root, the histogram is empty. Do you have an idea of how to fix this?

void test_open_roc(){
	TFile *f = new TFile("TMVA_250_300.root");
	TDirectory *f2 = (TDirectory*)f->Get("dataset;1");
	f2->cd();
	f2->ls();
	TDirectory *f3 = (TDirectory*)f2->Get("Method_Cuts;1");
	f3->cd();
	TDirectory *f4 = (TDirectory*)f3->Get("Cuts;1");
	f4->cd();
	TH1F *h = (TH1F*)f4->Get("MVA_Cuts_effBvsS");

	TFile * newf = new TFile("histTMVA_250_300.root","RECREATE");
	newf->cd();
	h->Write();
	newf->Close()
}

[couet]

@naikal_mc

I am trying to copy a histogram from file X.root to Y.root

The simplest way to do that is to use the command line tool rootcp

% rootcp --help
usage: rootcp [-h] [-c COMPRESS] [--recreate] [-r] [--replace] SOURCE [SOURCE ...] DEST

Copy objects from ROOT files into an other

positional arguments:
  SOURCE                Source file
  DEST                  Destination file

optional arguments:
  -h, --help            show this help message and exit
  -c COMPRESS, --compress COMPRESS
                        change the compression settings of the destination file (if not already existing).
  --recreate            recreate the destination file.
  -r, --recursive       recurse inside directories
  --replace             replace object if already existing

Note: If an object has been written to a file multiple times, rootcp will copy only the latest version of that object.

Examples:
- rootcp source.root dest.root
  Copy the latest version of each object in 'source.root' to 'dest.root'.

- rootcp source.root:hist* dest.root
  Copy all histograms whose names start with 'hist' from 'source.root' to 'dest.root'.

- rootcp source1.root:hist1 source2.root:hist2 dest.root
  Copy histograms 'hist1' from 'source1.root' and 'hist2' from 'source2.root' to 'dest.root'.

- rootcp --recreate source.root:hist dest.root
  Recreate 'dest.root' and copy the histogram named 'hist' from 'source.root' into it.

- rootcp -c 1 source.root:hist dest.root
  Change compression factor of 'dest.root' if not existing and copy the histogram named 'hist' from 'source.root' into it.

[pcanal]

@naikal_mc

	TFile * newf = new TFile("histTMVA_250_300.root","RECREATE");
	newf->cd();
	h->Write();
	newf->Close()

For the record you are missing the writing of the file

	TFile * newf = new TFile("histTMVA_250_300.root","RECREATE");
	newf->cd();
	h->Write();
	newf->Write();
	newf->Close()

[Wile_E_Coyote]

@naikal_mc Try:

{
  TFile *f = TFile::Open("TMVA_250_300.root");
  TH1F *h; f->GetObject("dataset/Method_Cuts/Cuts/MVA_Cuts_effBvsS", h);
  if (h) h->Print("base"); else std::cout << "No h!" << std::endl;
}

@pcanal Sorry, but you are wrong. Try:

{
  TFile *f = TFile::Open("hsimple.root");
  f->ls();
  TH1F *h; f->GetObject("hpx", h);
  // h->Print();
  TFile *newf = TFile::Open("hsimple.new.root", "RECREATE");
  h->Write();
  newf->ls();
  // newf->Close(); // not needed
  delete newf;
  delete f; // automatically deletes h, too
}