// RDataFrame add new column with Define does not follow manual?

using namespace ROOT;
RDataFrame df("T","htree.root");

// Try to plot the size of a vector object in the TTree.
// This one completely crashes root!
// auto h = df.Histo1D("vec_list.size()")
// ==> libc++abi.dylib: terminating with uncaught exception of type std::runtime_error: Unknown column: vec_list.size()

// FROM THE MANUAL
// Custom columns
//
//Custom columns are created by invoking Define(name, f, columnList). As usual, f can be any callable object
// (function, lambda expression, functor class...); it takes the values of the columns listed in columnList
// (a list of strings) as parameters, in the same order as they are listed in columnList.
// f must return the value that will be assigned to the temporary column.
// Comment: This appears not to be the case!! See below.

// We first need to create a new column with the vector size.
// Getting the size of a vector<> object, many different ways.
// For the vector size, this seems simplest:
auto dfplus0 = df.Define("num_list_size","vec_list.size()");

// Lambda function for the size of a vector<double>; !! Templated Lambda's not until c++20 !!
auto getsize_l = [](vector<double> &vec){ return vec.size(); };
// Using a Lambda function, the define needs special 3 args form:
auto dfplus1 = df.Define("num_list_size",getsize_l,{"num_list"});
// The 2 argument form does not work:
// auto dfplus = df.Define("num_list_size","getsize_l(num_list)");

// non-templated standard function. It does not matter if it is inline or not.
inline auto getsize_f(vector<double> &vec){ return vec.size(); };
auto dfplus2 = df.Define("num_list_size",getsize_f,{"num_list"});
// Again the 2 argument form does not work:
// auto dfplus = df.Define("num_list_size","getsize_f(num_list)");

// Templated (inline) standard function.
template<typename T> inline auto getsize( T& vec){ return vec.size();};
// The 3 argument form now crashes!
// auto dfplus = df.Define("num_list_size",getsize,{"num_list"});
// The 2 argument form now works!
auto dfplus3 = df.Define("num_list_size","getsize(num_list)");

auto h1 = dfplus0.Histo1D({"num_list_size","Vector Size 1",101u,-0.5,100.5},"num_list_size");
h1->SetLineColor(kRed); // This already triggers the LOOP!
h1->Draw();

// Accessing the X() component of the TVector3 in vec_list:
auto getX = [](vector<TVector3> &v){RVec<double> out; for( auto p: v) out.push_back(p.X()); return out;};
auto h2=df.Define("X",getX,{"vec_list"}).Histo1D("X")
h2->Draw();