When to call clear() in a vector of vectors

ROOT
1

Hi,

I have the following question. Say I am trying to fill a vector<vector > using the following:

  TFile *f = new TFile(file_name, "RECREATE");
  TTree *tree = new TTree("tree", "tree");
  tree->Branch("_parFloatVal","vector<vector<float> >", &_parFloatVal);

  std::vector<std::vector<float> > _parFloatVal;
  std::vector<float> floatVec;
  
  for (int i = 0; i < 10; i++) {
    _parFloatVal.clear();
    
    for (int j = 0; j < 10; j++) {
      floatVec.clear();

       for (int k = 0; k < 10; k++) {
           floatVec.push_back(old_vector->at(j)[k]); // just an example
      } // for (int k ...
       _parFloatVal.push_back(floatVec);
    } // for (int j ...
   
    tree->Fill();
  } // for (int i ...
  
  tree->Write();

Is the second clear() necessary (floatVec.clear()) in order to avoid pushing back elements to a vector that already has filled elements?

2

Try without “clearing” it :exclamation: :wink: :mrgreen: