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RDataFrame not able to read branches containing array whose size is of type Short_t

Dear ROOT community,

For repetitive plotting of many branches of a tree, I have been trying to shift my old (very lengthy) code using SetBranchAddress &Cie to the RDataFrame paradigms.
It seems very practical at first, but I met a problem that I could not solve, and ended up going back to the good old lengthy code.
The problem is that the variables that contain arrays of length “Reco_mu_size” cannot be read by the columnar analysis (TTreeReader) if the variable “Reco_mu_size” of the tree is of type Short_t.
So the simple histograming script attached works for variable “Centrality” (which is not an array), but not for variable “Reco_mu_nTrkHits” for example (on the attached .root file). It gives the error:

Error in <TTreeReaderValueBase::CreateProxy()>: The branch Reco_mu_size contains data of type short. It cannot be accessed by a TTreeReaderValue<int> terminate called after throwing an instance of 'std::runtime_error' what(): An error was encountered while processing the data. TTreeReader status code is: 6

I run with ROOT v6.22.02.

This seems like a rather simple functionality to implement, will it be done soon?

Best,
Guillaume
P.S: For now I don’t manage to attach my file… But here is the script MWE:

using namespace ROOT;
void test(){
  auto fnAOD = "Oniatree_AOD.root";
  ROOT::RDataFrame d("hionia/myTree", fnAOD);                                                                                                                                               
  auto test2 = d.Histo1D({"","",100,0,100},"Reco_mu_nTrkHits");

  TCanvas *c2 = new TCanvas("c2","c2",1500,1500);
  test2->Draw("hist");
}

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@eguiraud could you take a look please?

Hi @gfal,
ouch, I’m sorry for the misadventure!
Reading shorts works in general (see example program attached). The problem seems to be a bug in the type inference performed by RDF: it thinks Reco_mu_nTrkHits is an int but it is a short!

I fixed a similar bug in 6.22/02, could you check whether it’s fixed in the ROOT nightly builds?

Meanwhile, you can probably work around the problem by writing Histo1D<short>(...) instead of Histo1D(...), so that RDF does not have to infer the column type from the dataset.

Let us know if this resolves the issue!
Cheers,
Enrico

repro.cpp (557 Bytes)

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