/afs/cern.ch/work/a/aaltunda/public/www/CMSSW_5_3_13_patch3/src/PhysicsTools/PatExamples/bin/PatCOCExercise.cc

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#include <vector>

#include "TH1.h"
#include "TFile.h"
#include <TROOT.h>
#include <TSystem.h>

#include "DataFormats/Math/interface/deltaR.h"
#include "DataFormats/FWLite/interface/Event.h"
#include "DataFormats/Common/interface/Handle.h"
#include "DataFormats/PatCandidates/interface/Jet.h"
#include "FWCore/ParameterSet/interface/ProcessDesc.h"
#include "FWCore/FWLite/interface/AutoLibraryLoader.h"
#include "PhysicsTools/FWLite/interface/TFileService.h"
#include "FWCore/PythonParameterSet/interface/PythonProcessDesc.h"


//using namespace std;
//using namespace reco;
//using namespace pat;


int main(int argc, char *argv[]){
  // ----------------------------------------------------------------------
  // First Part: 
  //
  //  * enable the AutoLibraryLoader 
  //  * book the histograms of interest 
  //  * open the input file
  // ----------------------------------------------------------------------

  // load framework libraries
  gSystem->Load( "libFWCoreFWLite" );
  AutoLibraryLoader::enable();

  // only allow one argument for this simple example which should be the
  // the python cfg file
  if ( argc < 2 ) {
    std::cout << "Usage : " << argv[0] << " [parameters.py]" << std::endl;
    return 0;
  }

  // get the python configuration
  PythonProcessDesc builder(argv[1]);
  const edm::ParameterSet& fwliteParameters = builder.processDesc()->getProcessPSet()->getParameter<edm::ParameterSet>("FWLiteParams");

  // now get each parameter
  std::string   input_   ( fwliteParameters.getParameter<std::string  >("inputFile"  ) );
  std::string   output_  ( fwliteParameters.getParameter<std::string  >("outputFile" ) );
  std::string   overlaps_( fwliteParameters.getParameter<std::string  >("overlaps") );
  edm::InputTag jets_    ( fwliteParameters.getParameter<edm::InputTag>("jets"  ) );

  // book a set of histograms
  fwlite::TFileService fs = fwlite::TFileService(output_.c_str());
  TFileDirectory theDir = fs.mkdir("analyzePatCOC");
  TH1F* deltaRElecJet_ = theDir.make<TH1F>("deltaRElecJet" , "#DeltaR (elec, jet)"  ,  10,  0., 0.5);
  TH1F* elecOverJet_   = theDir.make<TH1F>("elecOverJet"   , "E_{elec}/E_{jet}"     , 100,  0.,  2.);
  TH1F* nOverlaps_     = theDir.make<TH1F>("nOverlaps"     , "Number of overlaps"   ,   5,  0.,  5.);
  
  // open input file (can be located on castor)
  TFile* inFile = TFile::Open(input_.c_str());

  // ----------------------------------------------------------------------
  // Second Part: 
  //
  //  * loop the events in the input file 
  //  * receive the collections of interest via fwlite::Handle
  //  * fill the histograms
  //  * after the loop close the input file
  // ----------------------------------------------------------------------

  // loop the events
  unsigned int iEvent=0;
  fwlite::Event ev(inFile); 
  for(ev.toBegin(); !ev.atEnd(); ++ev, ++iEvent){
    edm::EventBase const & event = ev;

    // break loop after end of file is reached 
    // or after 1000 events have been processed
    if( iEvent==1000 ) break;

    // simple event counter
    if(iEvent>0 && iEvent%1==0){
      std::cout << "  processing event: " << iEvent << std::endl;
    }

    // handle to jet collection
    edm::Handle<std::vector<pat::Jet> > jets;
    event.getByLabel(jets_, jets);

    // loop over the jets in the event
    for( std::vector<pat::Jet>::const_iterator jet = jets->begin(); jet != jets->end(); jet++ ){
      if(jet->pt()>20 && jet==jets->begin()){

        if(jet->hasOverlaps(overlaps_)){
          //get all overlaps
          const reco::CandidatePtrVector overlaps = jet->overlaps(overlaps_);
          nOverlaps_->Fill( overlaps.size() );
          //loop over the overlaps
          for( reco::CandidatePtrVector::const_iterator overlap = overlaps.begin(); overlap != overlaps.end(); overlap++){ 
            float deltaR = reco::deltaR( (*overlap)->eta(), (*overlap)->phi(), jet->eta(), jet->phi() );
            deltaRElecJet_->Fill( deltaR );
            elecOverJet_->Fill( (*overlap)->energy()/jet->energy() );
          }
        }
      }
    }
  }
  inFile->Close();
  return 0;
}