bool flag = false;
struct vecMaker
{
	std::vector<Double_t> operator()()
    {
        std::vector<Double_t> myVec{0,1,2,3,4,5};
        return myVec;
    }
};


ROOT::RDF::RNode ApplyDefines(ROOT::RDF::RNode df)
{
	if (flag)
	{
		return df.Define("y", [](){ return gRandom->Rndm(); });
	}
    flag = true;
	return ApplyDefines(df.Define("RVecColumn", vecMaker()));
}

void clipboard()
{
    ROOT::EnableImplicitMT();
    //first part of the 
    auto unifGen = [](double) { return gRandom->Uniform(-1.0, 1.0); };
    auto vGen = [&](int len)
    {
        ROOT::VecOps::RVec<Double_t> v(len);
        std::transform(v.begin(), v.end(), v.begin(), unifGen);
        return v;
    };

    ROOT::RDataFrame d(1024);
    auto outDF = d.Define("len", []() { return (int)gRandom->Uniform(0, 16); })
      .Define("x", vGen, {"len"});

    //ApplyDefines forces RDataFrame to save a column as a ROOT::VecOps::RVec<double>
	auto myNewDF = ApplyDefines(outDF);
    myNewDF.Snapshot("myDF", "mydf.root");

	TChain dEChain("myDF");
	dEChain.Add("mydf.root");

	ROOT::RDataFrame dEDF(dEChain);
	dEDF.Snapshot("analyzed", "newdf.root");
}