void dataframe_define_test_2()
{
	ROOT::EnableImplicitMT(30);
	TChain chains2("trees2");

	stringstream path;
	path<<"./test2.root";

	chains2.Add(path.str().c_str());
	ROOT::RDataFrame ds2(chains2);

	auto test=ds2.Define("theta",[](double z){
			if("MDz2<0"){
			return 1;
			}
			if("MDz2>0"){
			return 0;
			}
			},{"MDz2"}).Mean("theta");

	cout<<test.GetValue()<<endl;
}