Problem in accessing individual elements of an array branch through RDataFrame

ROOT
9

If this is not super performance-critical code, you can use the generic:

  std::vector<ROOT::RDF::RResultPtr<double>> means(1088);
  std::string branchName = "AnodeCurrent";
  for (int i = 0; i < 1088; ++i) {
    means[i] = df.Define("x", branchName + "[" + std::to_string(i) + "]")
                 .Mean("x");
  }

  for (auto m : means)
    std::cout << m.GetValue() << '\n';

And you can have several branch names in a vector<string> and have an outer loop over those.

If you need a version tweaked for performance we can work that out too, it will just require a bit more characters :slight_smile:

Cheers,
Enrico