for some work I need to use only one directory (EgammaV) instead of all wich are provided into a ROOT file.
With a small python script  I can do it but there is no significant file size reduction. For exemple if the initial size was 194 Mo, then at the end the final size is 180 Mo. Is it correct or is there an other operation I can do in order to reduce significantly the size.
P.S. if there is another way to get only the EgammaV branch, I would like to know it.
 : script
f_rel = ROOT.TFile(‘SomeROOTFile.root’, “UPDATE”)
t2 = f_rel.Get(“DQMData/Run 1”)
a = t2.GetListOfKeys()
for elem in a:
if (elem.GetTitle() == ‘EgammaV’):
name = elem.GetTitle() + “;1”
gDirectory.Delete(name) # → OK
ROOT Version: 6.22.08
Platform: linux, lxplus