Problems with OnPartialResultSlot in new ROOT version 6.32.02

[Juan_Alcaraz]

The following code (almost dummy for this example) was working in previous versions of ROOT (6.30.02), but not in a new one (6.32.02). Anybody knows what is going on ? Has the call tp OnPartialResultsSlot been changed? Should the registration of MyPrintEntries proceeed differently ?

Thanks, Juan

    def ShowEvolution(self, pos):
        # Declare function for printout (just once)
        if not ROOT.gROOT.GetGlobalFunction("MyPrintEntries"):
            ROOT.gInterpreter.Declare(
            """
            void MyPrintEntries(unsigned int iSlot, unsigned long long& iEvent){
                return;
            }
            """ 
            )

        # Set printout per file every nDump processed events
        nDump = 10000
        self.df[pos].Count().OnPartialResultSlot(nDump,ROOT.MyPrintEntries)

The error is:

    self.df[pos].Count().OnPartialResultSlot(nDump,ROOT.MyPrintEntries)
NotImplementedError: ROOT::RDF::RResultPtr<ULong64_t>& ROOT::RDF::RResultPtr<ULong64_t>::OnPartialResultSlot(ULong64_t everyNEvents, function<void(unsigned int,ULong64_t&)> callback) =>
    NotImplementedError: could not convert argument 2 (this method cannot (yet) be called)

[Danilo]

Dear Juan,

Thanks for the interesting post and welcome to the ROOT Community!
This seems to be an effect of the new version of cppyy, the interoperability engine behind PyROOT. I add in the loop our expert, @jonas .

Cheers,
D

[jonas]

Dear @Juan_Alcaraz,

I could reproduce this problem, with a simple reproducer. I opened an issue on GitHub so we don’t forget to fix it.

In the meantime, I can suggest you an alternative implementation, where the callback function is defined as a lambda function and passed around on the C++ side:

import ROOT

ROOT.gInterpreter.Declare(
"""
template<typename T>
ROOT::RDF::RResultPtr<T> &MyOnPartialResultSlot(
    ROOT::RDF::RResultPtr<T> &resultPtr,
    ULong64_t everyNEvents)
{
   auto myPrintEntries = [](unsigned int iSlot,
                            unsigned long long& iEvent) -> void
   {
      std::cout << "iEvent: " << iEvent << std::endl;
   };

   return resultPtr.OnPartialResultSlot(everyNEvents, myPrintEntries);
}
""" 
)

df = ROOT.RDataFrame(100).Define("x", "gRandom->Rndm()")

n_dump = 1

count = ROOT.MyOnPartialResultSlot(df.Count(), n_dump)

print(count.GetValue())

I hope this is good enough for now! This solution is also backwards compatible with older ROOT versions.

Cheers,
Jonas

[Juan_Alcaraz]

Thanks Jonas. Also for the fix, which works fine.

Best, Juan