GenericSelectorByValueMap.h

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#ifndef GenericSelectorByValueMap_h
#define GenericSelectorByValueMap_h

#include "FWCore/Framework/interface/Frameworkfwd.h"
#include "FWCore/Framework/interface/EDProducer.h"
#include "FWCore/Framework/interface/Event.h"
#include "FWCore/Framework/interface/EventSetup.h"
#include "FWCore/ParameterSet/interface/ParameterSet.h"
#include "FWCore/Utilities/interface/InputTag.h"
#include "DataFormats/Common/interface/ValueMap.h"
#include "DataFormats/Common/interface/View.h"

namespace edm {

namespace details {

  // which type should be used in edm::ParameterSet::getParameter<_> to read a parameter compatible with T ?

  // most types can use themselves
  template <typename C>
  struct CompatibleConfigurationType {
    typedef C type;
  };

  // "float" is not allowed, as it conflicts with "double"
  template <>
  struct CompatibleConfigurationType<float> {
    typedef double type;
  };

} // namespace details;

template <typename T, typename C>
class GenericSelectorByValueMap : public edm::EDProducer {
public:
  explicit GenericSelectorByValueMap(edm::ParameterSet const & config);

private:
  typedef T candidate_type;
  typedef C selection_type;
  typedef typename details::template CompatibleConfigurationType<selection_type>::type cut_type;

  void produce(edm::Event & event, edm::EventSetup const & setup) override;

  edm::EDGetTokenT<edm::View<candidate_type> >      token_electrons;
  edm::EDGetTokenT<edm::ValueMap<selection_type> >  token_selection;

  cut_type m_cut;
};

} // namespace edm;

//------------------------------------------------------------------------------

#include <vector>
#include <memory>

#include "DataFormats/Common/interface/Handle.h"
#include "DataFormats/Common/interface/Ptr.h"
#include "DataFormats/Common/interface/PtrVector.h"
#include "DataFormats/Common/interface/RefToBaseVector.h"

//------------------------------------------------------------------------------

namespace edm {

template <typename T, typename C>
GenericSelectorByValueMap<T,C>::GenericSelectorByValueMap(edm::ParameterSet const & config) :
  token_electrons(consumes<edm::View<candidate_type> >(config.getParameter<edm::InputTag>("input"))),
  token_selection(consumes<edm::ValueMap<selection_type> >(config.getParameter<edm::InputTag>("selection"))),
  m_cut(config.getParameter<cut_type>("cut"))
{
  // register the product
  produces<edm::RefToBaseVector<candidate_type> >();
}

//------------------------------------------------------------------------------

template <typename T, typename C>
void GenericSelectorByValueMap<T, C>::produce(edm::Event & event, const edm::EventSetup & setup)
{
  auto candidates = std::make_unique<edm::RefToBaseVector<candidate_type>>();

  // read the collection of GsfElectrons from the Event
  edm::Handle<edm::View<candidate_type> > h_electrons;
  event.getByToken(token_electrons, h_electrons);
  edm::View<candidate_type> const & electrons = * h_electrons;

  // read the selection map from the Event
  edm::Handle<edm::ValueMap<selection_type> > h_selection;
  event.getByToken(token_selection, h_selection);
  edm::ValueMap<selection_type> const & selectionMap = * h_selection;

  for (unsigned int i = 0; i < electrons.size(); ++i) {
    edm::RefToBase<candidate_type> ptr = electrons.refAt(i);
    if (selectionMap[ptr] > m_cut)
     candidates->push_back(ptr);
  }

  // put the product in the event
  event.put(std::move(candidates));
}

} // namespace edm;

#endif // GenericSelectorByValueMap_h