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ROOT Version: 6.20
Platform: MacOS
Compiler: Clang
Dear ROOT developers,
I do not know wether this is a known behavior, or even something trivial. I was working on some TTrees when I noticed that RDataFrame shows some issues working with branches whose name and leaflist do not coincide, that is, for instance:
TTree tree ("tree", "tree");
int y;
tree.Branch ("x0", &y, "x0/I"); // Good
tree.Branch ("x1", &y, "z1/I"); // Not good
In particular, importing the TTree as a RDataFrame will produce two columns named respectively “x0” and “x1.z1”. This leads to errors using functions like Snapshot or Histo1D.
I attach a short macro which shows the problem. It creates a TTree and saves it to a TFile. Then it opens that TFile both in the standard ROOT way and with RDF, prints the columns’ names, draws a histogram of the variable x1 and saves the file again.
void CreateFileAndTree() // Create a dummy file and TTree
{
TFile file ("dummy.root", "RECREATE");
TTree tree ("tree", "tree");
int y;
tree.Branch ("x0", &y, "x0/I"); // HERE! x1 == x1 --> OK
tree.Branch ("x1", &y, "z1/I"); // HERE! x1 != z1 --> NO --> Problems with snapshot
for (y = 0; y < 100; y++) tree.Fill();
tree.Write();
file.Close();
}
void ttree_Macro()
{
CreateFileAndTree(); // Create a dummy file and TTree
// --- Standard ROOT
// Read Tree
TFile *fileIn = new TFile ("dummy.root", "READ");
TFile *fileOut = new TFile ("dummyROOT.root", "RECREATE");
TTree *tree;
fileIn -> GetObject("tree", tree);
// Print info
tree -> Print(); // Print info, including column names
// Draw a histogram
tree -> Draw ("x1"); // Draw a histogram - WORKS!
// Save Tree
tree -> Write();
fileOut -> Close();
fileIn -> Close();
// --- RDataFrame
// Read Tree
ROOT::RDataFrame d ("tree", "dummy.root");
// Print info
for (auto && elem : d.GetColumnNames()) std::cout << elem << std::endl; // Print columns names
// Draw a histogram
auto h = d.Histo1D("x1");
h -> Draw(); // Draw a histogram - DOES NOT WORK
// Save Tree
d.Snapshot("tree", "dummyRDF.root", d.GetColumnNames()); // WORKS!
d.Snapshot("tree", "dummyRDF.root"); // DOES NOT WORK!
}
I am looking forward to your reply.
Best regards,
Loris