Vertex collection syntax

[OtaviusDecius]

Hi there,

I am trying to find the definition for the at(0) while accessing a vertex collection.
For instance,

      MyVertex& primaryVertex = vertex_coll->at(0);
      histosTH1F["prim_vtx_zpos"]->Fill( primaryVertex.z, event_weight );
      histosTH1F["prim_vtx_xpos"]->Fill( primaryVertex.x, event_weight );
      histosTH1F["prim_vtx_ypos"]->Fill( primaryVertex.y, event_weight );

Does 0 in at(0) mean primary vertex? What about at(1)?

thanks in advance,
Luiz

[Axel]

Hi Luiz,
Where does that code come from?
Axel.

[OtaviusDecius]

It comes from CMS analysis code:

//STANDARD ROOT INCLUDES
#include <TROOT.h>
#include <TH1.h>
#include <TH2.h>
#include <TProfile.h>
#include <TStyle.h>
#include <TCanvas.h>
#include <TTree.h>
#include <TFile.h>
#include <TChain.h>
#include <TChainElement.h>
#include <TDirectory.h>
#include “MyVertex.h”
//STANDARD C++ INCLUDES
#include
#include
#include
#include
#include
#include
#include

map<string,TH1F*> histosTH1F;

// Vertices
int n_vertices_selected = 0;
/int idx_vtx_max_sumpt = -1;
double sumpt_max = 0.;/
for(vector::iterator it_vtx = vertex_coll->begin() ; it_vtx != vertex_coll->end() ; ++it_vtx){
int idx_vtx = it_vtx - vertex_coll->begin();
//if( it_vtx->SumPtTracks > sumpt_max ){ idx_vtx_max_sumpt = idx_vtx; sumpt_max = it_vtx->SumPtTracks; }

     if( it_vtx->fake ) continue;
     if( !it_vtx->validity ) continue;
     ++n_vertices_selected;

     histosTH1F["vtx_zpos"]->Fill( it_vtx->z, event_weight );
     histosTH1F["vtx_xpos"]->Fill( it_vtx->x, event_weight );
     histosTH1F["vtx_ypos"]->Fill( it_vtx->y, event_weight );
     histosTH1F["vtx_ndof"]->Fill( it_vtx->ndof, event_weight );
     histosTH1F["vtx_chi2"]->Fill( it_vtx->chi2, event_weight );
  }
  //histosTH1F["vtx_sumpt_max"]->Fill( idx_vtx_max_sumpt, event_weight );
  histosTH1F["vertex_multiplicity"]->Fill( n_vertices_selected, event_weight );

  MyVertex& primaryVertex = vertex_coll->at(0);
  histosTH1F["prim_vtx_zpos"]->Fill( primaryVertex.z, event_weight );
  histosTH1F["prim_vtx_xpos"]->Fill( primaryVertex.x, event_weight );
  histosTH1F["prim_vtx_ypos"]->Fill( primaryVertex.y, event_weight );

But I have just found it:

MyPUSumInfo.cc: cout << " --> zposition : " << zposition.at(ivtx) << endl;

slight_smile:

Thanks,
Luiz

[Axel]

Nonetheless, my answer also for future reference:

The code and the data format use ROOT, but ROOT does not define it. So we cannot possibly tell what’s at index 0, you should instead ask those who provide your data or code!

Cheers, Axel

[OtaviusDecius]

Dear Axel,

I have found the answer:

std::array::at

reference at ( size_type n );
const_reference at ( size_type n ) const;

Access element

Returns a reference to the element at position n in the array.
The function automatically checks whether n is within the bounds of valid elements in the container, throwing an out_of_range exception if it is not (i.e., if n is greater than, or equal to, its [size](http://www.cplusplus.com/array::size)). This is in contrast with member operator[], that does not check against bounds.

Thanks for your attention,
Luiz

[Axel]

That does not say where the primary vertex is. That would be part of your data model, at I explained.

Cheers, Axel