LowPtGSFToTrackLinker.cc

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#include <string>

#include "DataFormats/Candidate/interface/Candidate.h"
#include "DataFormats/ParticleFlowCandidate/interface/PFCandidate.h"
#include "DataFormats/ParticleFlowCandidate/interface/PFCandidateFwd.h"
#include "DataFormats/GsfTrackReco/interface/GsfTrack.h"
#include "DataFormats/GsfTrackReco/interface/GsfTrackFwd.h"
#include "DataFormats/Common/interface/Association.h"
#include "FWCore/Framework/interface/global/EDProducer.h"
#include "FWCore/Framework/interface/Event.h"
#include "FWCore/Framework/interface/EventSetup.h"
#include "FWCore/Framework/interface/Frameworkfwd.h"
#include "FWCore/ParameterSet/interface/ParameterSet.h"
#include "FWCore/Utilities/interface/Exception.h"
#include "DataFormats/ParticleFlowReco/interface/PreId.h"
#include "DataFormats/ParticleFlowReco/interface/PreIdFwd.h"
#include "DataFormats/EgammaReco/interface/ElectronSeed.h"
#include "DataFormats/EgammaReco/interface/ElectronSeedFwd.h"
#include "DataFormats/EgammaReco/interface/ElectronSeedFwd.h"
#include "DataFormats/TrackReco/interface/Track.h"
#include "FWCore/Framework/interface/MakerMacros.h"

class LowPtGSFToTrackLinker : public edm::global::EDProducer<> {
public:
    explicit LowPtGSFToTrackLinker(const edm::ParameterSet&);
    ~LowPtGSFToTrackLinker() override;
    
    void produce(edm::StreamID, edm::Event&, const edm::EventSetup&) const override;
    static void fillDescriptions(edm::ConfigurationDescriptions&);
   
private:
    const edm::EDGetTokenT<reco::TrackCollection>          tracks_;
    const edm::EDGetTokenT< std::vector<reco::PreId> > preid_;  
    const edm::EDGetTokenT< std::vector<reco::GsfTrack> > gsftracks_;   
};

LowPtGSFToTrackLinker::LowPtGSFToTrackLinker(const edm::ParameterSet& iConfig) :
  tracks_{consumes<reco::TrackCollection>(iConfig.getParameter<edm::InputTag>("tracks"))},
  preid_{consumes<std::vector<reco::PreId> >(iConfig.getParameter<edm::InputTag>("gsfPreID"))},
  gsftracks_{consumes<std::vector<reco::GsfTrack> >(iConfig.getParameter<edm::InputTag>("gsfTracks"))} {     
        produces< edm::Association<reco::TrackCollection> > ();
    }

LowPtGSFToTrackLinker::~LowPtGSFToTrackLinker() {}

void LowPtGSFToTrackLinker::produce(edm::StreamID, edm::Event& iEvent, const edm::EventSetup& iSetup) const {
    edm::Handle<std::vector<reco::GsfTrack> > gsftracks;
    iEvent.getByToken(gsftracks_, gsftracks);

    edm::Handle<reco::TrackCollection> tracks;
    iEvent.getByToken(tracks_, tracks);

    edm::Handle<std::vector<reco::PreId> > preid;
    iEvent.getByToken(preid_, preid);

    // collection sizes, for reference
    const size_t ngsf = gsftracks->size();

    //store mapping for association
    std::vector<int> gsf2track(ngsf, -1);

    //map Track --> GSF and fill GSF --> PackedCandidates and GSF --> Lost associations
    for(unsigned int igsf=0; igsf < ngsf; ++igsf) {
        reco::GsfTrackRef gref(gsftracks, igsf);
        reco::TrackRef trk = preid->at(
            gref->seedRef().castTo<reco::ElectronSeedRef>().index()
            ).trackRef();

        if(trk.id() != tracks.id()) {
            throw cms::Exception("WrongCollection", "The reco::Track collection used to match against the GSF Tracks was not used to produce such tracks");
        }

        size_t trkid = trk.index();
        gsf2track[igsf] = trkid;
    }

    // create output collections from the mappings
    auto assoc = std::make_unique< edm::Association<reco::TrackCollection> >(tracks);
    edm::Association<reco::TrackCollection>::Filler filler(*assoc);
    filler.insert(gsftracks, gsf2track.begin(), gsf2track.end());
    filler.fill();
    iEvent.put(std::move(assoc));
}

void LowPtGSFToTrackLinker::fillDescriptions(edm::ConfigurationDescriptions& descriptions) {
    edm::ParameterSetDescription desc;
    desc.add<edm::InputTag>("tracks", edm::InputTag("generalTracks"));
    desc.add<edm::InputTag>("gsfPreID", edm::InputTag("lowPtGsfElectronSeeds"));
    desc.add<edm::InputTag>("gsfTracks", edm::InputTag("lowPtGsfEleGsfTracks"));
    descriptions.add("lowPtGsfToTrackLinksDefault", desc);
}

DEFINE_FWK_MODULE(LowPtGSFToTrackLinker);