Reading branches with variable length arrays

ROOT
1

Hi,

in my tree I have a bunch of arrays that I created with
mytree->Branch(“Muon_N”,&Muon_N,“Muon_N/I”);
mytree->Branch(“Muon_E”,Muon_E,“Muon_N[Muon_N]/D”);

When I read my tree, I only load in single branches to speed up things. I randomly access my variables and it happens sometimes that I request (i.e. Branch->GetEntry) the Muon_E before I access Muon_N. In that case I end up with a Muon_E which is empty. If I reverse the order I get an non-empty Muon_E (if Muon_N>0).

So is there a way to obtain the “counting” variable (i.e. Muon_N) to get the corresponding entry before I actually access Muon_E?

Thanks
Duc

2

Hi,

Use:TBranch *b = mytree->GetBranch("Muon_E"); TLeaf *l = (TLeaf*)b->GetListOfLeaves()->At(0); if (l->GetLeafCount()) { l->GetLeafCount()->GetBranch()->GetEntry(entry); }

Cheers,
Philippe