Add multiple candidate info with a switch

Phys/FunTuple/src/FunTuple.cpp

@@ -222,6 +222,10 @@ protected:
   // function for filling void functors
   void fill_void_func_output( const Tuples::Tuple& ntuple ) const;
 
+  // function for filling multiple candidate info
+  void fill_multiple_cand_info( const Tuples::Tuple& ntuple, const std::size_t totcand,
+                                const unsigned int icand ) const;
+
   // function for filling loki functors
   void fill_loki_func_output( const typename LHCb::InputTypeSignature<T>::LoKiItemType& cand,
                               const unsigned int& nfield, const Tuples::Tuple& ntuple ) const;
@@ -267,6 +271,10 @@ private:
   Gaudi::Property<std::vector<std::string>> m_preamble_def_loki{this, "loki_preamble", {}, "List of preamble strings"};
   std::string                               m_preamble_loki;
 
+  /// boolean to store multiple candidate information (default: false)
+  Gaudi::Property<bool> m_store_multiple_cand_info{this, "store_multiple_cand_info", false,
+                                                   "Store the candidate index and the total number of candidates"};
+
   //// Loki functor factory
   ToolHandle<typename LHCb::InputTypeSignature<T>::LoKiFactory> m_factory_loki = {
       LHCb::InputTypeSignature<T>::LoKiFactoryString, this};
@@ -694,12 +702,18 @@ void FunTupleBase<T>::write_tuple( const LHCb::FTuple::retype<T>& vector_of_cand
   if ( this->msgLevel( MSG::DEBUG ) ) { debug << "write_tuple: Candidates found booking their info" << endmsg; }
   Tuples::Tuple ntuple = this->nTuple( m_ntupleTname );
 
-  for ( unsigned int ncand = 0; ncand < vector_of_cands[0].size(); ncand++ ) { // number of cands (write tuple)
+  // total number of candidates
+  std::size_t totcand{vector_of_cands[0].size()};
+  for ( unsigned int icand = 0; icand < vector_of_cands[0].size(); icand++ ) { // number of cands (write tuple)
+    // if requested store the total number of candidates and the candidate index
+    if ( m_store_multiple_cand_info ) fill_multiple_cand_info( ntuple, totcand, icand );
+
+    // fill void functors
     fill_void_func_output( ntuple );
     for ( unsigned int nfield = 0; nfield < vector_of_cands.size();
           nfield++ ) { // number of fields i.e decay descriptors
       // get the particle
-      const auto cand = vector_of_cands[nfield][ncand];
+      const auto cand = vector_of_cands[nfield][icand];
       // fill loki functors
       if ( !m_all_empty_lokifuncs ) fill_loki_func_output( *cand, nfield, ntuple );
       // fill thor functors
@@ -733,7 +747,14 @@ void FunTupleBase<T>::write_tuple( const LHCb::FTuple::retype<T>& vector_of_cand
   // Hard code "nfield" to zero ie head of the decay here
   unsigned int nfield{0};
   auto const   iterable = LHCb::Event::make_zip<SIMDWrapper::Scalar>( vector_of_cands );
+  // total number of candidates
+  std::size_t  totcand{vector_of_cands.size()};
+  unsigned int icand{0};
   for ( auto const& cand : iterable ) { // number of cands (write tuple)
+    // if requested store the total number of candidates and the candidate index
+    if ( m_store_multiple_cand_info ) fill_multiple_cand_info( ntuple, totcand, icand );
+
+    // fill void functors
     fill_void_func_output( ntuple );
     // fill thor functors
     if ( !m_all_empty_thorfuncs ) fill_thor_func_output( cand, nfield, ntuple );
@@ -741,6 +762,9 @@ void FunTupleBase<T>::write_tuple( const LHCb::FTuple::retype<T>& vector_of_cand
     if ( this->msgLevel( MSG::DEBUG ) ) { debug << "write_tuple: Writing tuple after booking" << endmsg; }
     StatusCode sc_write = ntuple->write();
     if ( sc_write.isFailure() ) { this->err() << "Unable to write the tuple" << endmsg; }
+
+    // increment counter
+    ++icand;
   }
 }
 
@@ -771,6 +795,23 @@ void FunTupleBase<T>::fill_void_func_output( const Tuples::Tuple& ntuple ) const
   }
 }
 
+template <class T>
+void FunTupleBase<T>::fill_multiple_cand_info( const Tuples::Tuple& ntuple, const std::size_t totcand,
+                                               const unsigned int icand ) const {
+  // A warning is raised by GaudiTupleAlg about "'unsigned long' has different sizes on 32/64 bit systems, casting
+  // 'totCandidates' to 'unsigned long long'". To avoid this warning thrown after event loop, we cast the size_t to
+  // unsigned long long here itself.
+  // See also issue: https://gitlab.cern.ch/lhcb/DaVinci/-/issues/48
+  StatusCode sc_totcand = ntuple->column( "totCandidates", static_cast<unsigned long long>( totcand ) );
+  if ( sc_totcand.isFailure() )
+    throw GaudiException( "Error booking the total number of candidates (totCandidates)", "write_tuple",
+                          StatusCode::FAILURE );
+
+  StatusCode sc_ncand = ntuple->column( "nCandidate", icand );
+  if ( sc_ncand.isFailure() )
+    throw GaudiException( "Error booking the candidate number (nCandidate)", "write_tuple", StatusCode::FAILURE );
+}
+
 template <class T>
 void FunTupleBase<T>::fill_loki_func_output( const typename LHCb::InputTypeSignature<T>::LoKiItemType& cand,
                                              const unsigned int& nfield, const Tuples::Tuple& ntuple ) const {