RDataFrame::Vary(...) usage documentation

krasznaa · January 22, 2024, 12:38pm

Dear All,

Now for the very first time, I’m trying to see how RDataFrame::Vary could be used in an “ATLAS analysis”. I may very well not be the first one to try this, though I haven’t seen any presentations in the experiment yet on people having done this successfully yet.

I’m embarrassed to say how long it took me to figure out exactly how I should implement some functors that could be used with RDF::Vary...). But I think by now I managed.

github.com

krasznaa/atlas-tool-example/blob/main/MuonAnalysisTools/MuonAnalysisTools/MuonCalibratorRDF.h#L46-L73


      
          /// Functor that could be used directly with @c ROOT::RDataFrame::Vary
          class MuonVariator : public ATE::MuonCalibrator {
          
          public:
              // Inherit the base class's constructor(s).
              using ATE::MuonCalibrator::MuonCalibrator;
          
              /// Operator applying the calibration to a single muon
              ROOT::RVec<std::vector<float> > operator()(
                  const std::vector<float>& pt, const std::vector<float>& eta,
                  const std::vector<float>& phi) const;
          
          };  // class MuonVariator
          
          /// Functor that could be used with @c ROOT::RDataFrame::Vary, on an xAOD
          class MuonVariatorxAOD : public ATE::MuonCalibrator {
          
          public:
              // Inherit the base class's constructor(s).
              using ATE::MuonCalibrator::MuonCalibrator;

This file has been truncated. show original

The reason I’m opening this thread is because I found the documentation of the support for systematic variations in RDF a bit lacking. I gathered by now that this is still an experimental feature in the code, but the documentation is not even clear about that. For instance it took me a moment to find that the code example in ROOT: ROOT::RDF::RInterface< Proxied, DataSource > Class Template Reference should rather look like:

auto hx = ROOT::RDF::Experimental::VariationsFor(nominal_hx);

Since even in the master branch that function is still in the Experimental namespace.

github.com

root-project/root/blob/master/tree/dataframe/inc/ROOT/RDFHelpers.hxx#L219


      
          //
          // An overview of how systematic variations work internally. Given N variations (including the nominal):
          //
          // RResultMap   owns    RVariedAction
          //  N results            N action helpers
          //                       N previous filters
          //                       N*#input_cols column readers
          //
          // ...and each RFilter and RDefine knows for what universe it needs to construct column readers ("nominal" by default).
          template <typename T>
          RResultMap<T> VariationsFor(RResultPtr<T> resPtr)
          {
             R__ASSERT(resPtr != nullptr && "Calling VariationsFor on an empty RResultPtr");
          
             // populate parts of the computation graph for which we only have "empty shells", e.g. RJittedActions and
             // RJittedFilters
             resPtr.fLoopManager->Jit();
          
             std::unique_ptr<RDFInternal::RActionBase> variedAction;
             std::vector<std::shared_ptr<T>> variedResults;

But don’t understand my complaints too negatively. I really appreciate the work on this RDF feature. I just wonder if more discussion between ATLAS and the ROOT team could benefit this code.

Cheers,
Attila

ROOT Version: 6.28/10
Platform: Linux
Compiler: GCC 13

jonas · January 22, 2024, 1:07pm

Hi @krasznaa, thanks a lot for your detailed report!

I invite @mczurylo to take a look and improve the documentation accordingly

mczurylo · January 22, 2024, 2:05pm

Hi @krasznaa,

Thanks a lot for your insightful comment. I can clearly see your point, the documentation will be improved ASAP.

I just wonder if more discussion between ATLAS and the ROOT team could benefit this code.

Sure, we are always open to hear what are the ATLAS needs regarding RDF. We can discuss more details offline via email/MM.

Have a nice day!

Cheers,
Marta

system · February 5, 2024, 2:05pm

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