Some values in map<string, double> being written as NaN

saving a std::map< string, double> via RDF Snaphot method returns some values in the tail of the frame as NaN.

Warning message during runtime:

Warning in <TTree::CopyEntries>: The export branch and the import branch do not have the same streamer type. (The branch name is triggerMap.first.)

ROOT Version: 6.18/00
Platform: CentOS 7.7.1908
Compiler: gcc8

Hi Lucas,
I can’t reproduce the behavior with the minimal reproducer below.

Could you please provide a minimal reproducer or amend mine so that it shows the problem?


#include <map>
#include <string>
#include <ROOT/RDataFrame.hxx>

std::map<std::string, double> get_map()
   return std::map<std::string, double>({{"one", 1.}, {"two", 2.}});

int main()
   ROOT::RDataFrame(10).Define("x", get_map).Snapshot("t", "f.root");
   return 0;


I’m working on a minimal version, sorry it is taking so long.

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