RDF Define at PyROOT using C++ code not working

[imanol097]

I am trying to define some RVec variable using C++ syntax into PyROOT rdf. Basically some operation with track momentums (tr_px, tr_py).

ROOT.gInterpreter.Declare('''
                          std::vector<float> make_pT_RVec(std::vector<float> tr_px, std::vector<float> tr_py){

                          const auto size = tr_px.size();
                          std::vector<float> pT_RVec(size);

                          for (size_t i=0; i < size; ++i) {
                              pT_RVec[i] = tr_px[i]*tr_px[i]+tr_py[i]*tr_py[i]; 
                            }

                         return pT_RVec;
                         }''')

new_rdf = rdf.Define("pT_RVec", "make_pT_RVec(tr_px, tr_py)")

It gives an error that I don’t understand:

runtime_error: Template method resolution failed:
  ROOT::RDF::RInterface<ROOT::Detail::RDF::RRange<ROOT::Detail::RDF::RLoopManager>,void> 
ROOT::RDF::RInterface<ROOT::Detail::RDF::RRange<ROOT::Detail::RDF::RLoopManager>,void>::Define(basic_string_view<char,char_traits<char> > name, basic_string_view<char,char_traits<char> > expression) =>
    runtime_error: 
RDataFrame: An error occurred during just-in-time compilation. The lines above might indicate the cause of the crash
 All RDF objects that have not run an event loop yet should be considered in an invalid state.

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ROOT Version: Not Provided
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[RENATO_QUAGLIANI]

The function signature seems wrong, should be something like

std::vector<float> myfunction(std::vector<float> input1,...){
...
}

std::vector alone is likely the reason of the crash.
Cheers

Edit: I saw you modified the original post, are you sure the branches you try to process have the vector signature?

You can check

df.GetColumnType("tr_px")

If they are RVec, try to change the signature of the function arguments.

[imanol097]

Yes. I think that was the problem. I put the wrong type, it was an RVec.

Thanks you @RENATO_QUAGLIANI

[RENATO_QUAGLIANI]

@imanol097

make_pT_RVec(std::vector<float> tr_px, std::vector<float> tr_py){

not sure if it’s automatically handled, but when i need to combine RVec object with custom function i always avoid to make copies for each call , with const even better if possible

make_pT_RVec(const RVec<float> & tr_px, const RVec<float> tr_py){

A thing you can also bare in mind is that if you would have done

Define( "pt2", "tr_px*tr_px + tr_py*tr_py")

RDF is smart enough to provide vector[size] * vector[size] = product-element wise or also with vector*scalar. Not sure if the pow( RVec<T>, 0.5 ) is also implemented (apparently yes, see next comment) , if so you would not even need to declare your function

[RENATO_QUAGLIANI]

Just testeed on ROOT prompt,

root [3] ROOT::VecOps::RVec<double> a{1,2,3};
root [4] ROOT::VecOps::RVec<double> b{2,4,2};
root [5] a*b
(ROOT::VecOps::RVec<decltype(v0[0] * v1[0])>) { 2.0000000, 8.0000000, 6.0000000 }
root [6] pow( (a*a + b*b),0.5)
(ROOT::VecOps::RVec<PromoteTypes<double, double> >) { 2.2360680, 4.4721360, 3.6055513 }

seems it’s implemented .
You could have simply done :

Define( "tr_pt" , "pow( tr_px * tr_px + tr_py * tr_py , 0.5)")
//or Define( "tr_pt" , "sqrt( tr_px * tr_px + tr_py * tr_py )")

[imanol097]

Yes I know. This was the starting point of a more complex custom function.
Thank you

[imanol097]

Good point! Thank you