Iterating over histograms defined in current ROOT session?

ROOT
1

Hi,

I’d like to do something like in hadd.C, but for the histograms from the current ROOT session. Is there a way of accessing all currently defined TH1 objects - there should be, since ROOT provides tab completion for variable names?
Then, I could do something like:
TIter nextkey( gROOT->GetListOfKeys() );

TKey *key, oldkey=0;
UInt_t numKey = 0;
cout << “Before loop.” << endl;
while ( (key = (TKey)nextkey())) {
TObject *obj = key->ReadObj();
cout << “Key #” << numKey << ", object pointer: " << obj << endl;

if ( obj->IsA()->InheritsFrom( "TH1" ) ) {

  TH1 *h1 = (TH1*)obj;

  cout << h1->GetName() << endl;
  // ...
  }
  ++numKey;

}

Thanks,
Holger

2

Hi,

if you created them all in the same place then you can access all histograms from gDirectory (an object of type TDirectory), the way you described.

Cheers, Axel.

3

Hi,

a colleague from ATLAS (Tayfun Ince incet@uvic.ca) has found a working solution:
TObject* obj = 0;
TIter next(gPad->GetListOfPrimitives());
while ( obj = (TObject*)next() ) {
if ( obj->InheritsFrom(TH1::Class()) ) {
TH1* h1d = (TH1*)obj;
}
}

Thanks,
Holger

4

Hi,

yes, that works well for all histograms drawn on a given pad; gDirectory->GetList() will iterate over all objects created in all canvases in the current directory.

For completeness: if you want to iterate only over the drawn histograms, you can loop over all pads using gROOT->GetListOfCanvases().

Cheers, Axel.