Failing tokenizing expression in RDataFrame's Take

[zenith378]

Dear all,
I am having some issues with the option Take in RDataFrame.
I have an action (two filters and a Take) to repeat on multiple columns with similar names of the same dataframe, so I implemented some for loops:

auto d1 = ROOT::RDataFrame("Events", "./../trees/tree_general_cut.root");
for (int k = -120; k <= 120; k += 20)
   {
      if (k == 0)
         continue;
      std::string_view data_name = "nominal_z==" + std::to_string(k);
      for (int j = 0; j < 20; j++)
      {
         std::string_view filter_name = "rdfentry_ % 20 ==" + std::to_string(j);
         auto data = new Double_t[n];
         for (int i = 1; i < 27; i++)
         {
            std::string_view column_name = "numclusterod" + std::to_string(i);
            auto v1 = Mean(d1.Filter(data_name)
                          .Filter(filter_name)
                          .Take<double, ROOT::VecOps::RVec<double>>(column_name)
                          .GetValue());
          }
       }
    }

Executing the macro, it seems that the method Take has some problems with the string I passed to it.

libc++abi.dylib: terminating with uncaught exception of type std::runtime_error: Failed to tokenize expression:
numclusterod1

It seems strange that I don’t have problem passing a filter defining a string, but I cannot make the same operation with the action Take().

Does anyone have an idea of what this might be?
Thanks a lot.

---

_ROOT Version: 6.26/06
_Platform: macOS 10.15.7
_Compiler: clang-1200.0.32.29

---

[eguiraud]

Hi @zenith378 ,

@zenith378

std::string_view data_name = "nominal_z==" + std::to_string(k);

here you are building a string_view that will point to the storage of the temporary std::string that is destroyed right after this line. I think this might be the problem (RDF likely ends up reading garbage from those strings).

Try making those string_view actual std::strings, that might help.

Otherwise please share a small self-contained reproducer that we can run on our side to debug what is happening.

Cheers,
Enrico