hvector.C File Reference

Detailed Description

Write and read STL vectors in a tree.

 
#include <vector>
 
#include "TFile.h"
#include "TTree.h"
#include "TCanvas.h"
#include "TFrame.h"
#include "TH1F.h"
#include "TBenchmark.h"
#include "TRandom.h"
#include "TSystem.h"
 
void write()
{
 
   TFile *f = TFile::Open("hvector.root","RECREATE");
 
   if (!f) { return; }
 
   // Create one histograms
   TH1F *hpx = new TH1F("hpx","This is the px distribution",100,-4,4);
   hpx->SetFillColor(48);
 
   std::vector<float> vpx;
   std::vector<float> vpy;
   std::vector<float> vpz;
   std::vector<float> vrand;
 
   // Create a TTree
   TTree *t = new TTree("tvec","Tree with vectors");
   t->Branch("vpx",&vpx);
   t->Branch("vpy",&vpy);
   t->Branch("vpz",&vpz);
   t->Branch("vrand",&vrand);
 
   // Create a new canvas.
   TCanvas *c1 = new TCanvas("c1","Dynamic Filling Example",200,10,700,500);
 
   gRandom->SetSeed();
   const Int_t kUPDATE = 1000;
   for (Int_t i = 0; i < 25000; i++) {
      Int_t npx = (Int_t)(gRandom->Rndm(1)*15);
 
      vpx.clear();
      vpy.clear();
      vpz.clear();
      vrand.clear();
 
      for (Int_t j = 0; j < npx; ++j) {
 
         Float_t px,py,pz;
         gRandom->Rannor(px,py);
         pz = px*px + py*py;
         Float_t random = gRandom->Rndm(1);
 
         hpx->Fill(px);
 
         vpx.emplace_back(px);
         vpy.emplace_back(py);
         vpz.emplace_back(pz);
         vrand.emplace_back(random);
 
      }
      if (i && (i%kUPDATE) == 0) {
         if (i == kUPDATE) hpx->Draw();
         c1->Modified();
         c1->Update();
         if (gSystem->ProcessEvents())
            break;
      }
      t->Fill();
   }
   f->Write();
 
   delete f;
}
 
 
void read()
{
 
   TFile *f = TFile::Open("hvector.root","READ");
 
   if (!f) { return; }
 
   TTree *t; f->GetObject("tvec",t);
 
   std::vector<float> *vpx = nullptr;
 
  // Create a new canvas.
   TCanvas *c1 = new TCanvas("c1","Dynamic Filling Example",200,10,700,500);
 
   const Int_t kUPDATE = 1000;
 
   TBranch *bvpx = nullptr;
   t->SetBranchAddress("vpx",&vpx,&bvpx);
 
 
   // Create one histograms
   TH1F *h = new TH1F("h","This is the px distribution",100,-4,4);
   h->SetFillColor(48);
 
   for (Int_t i = 0; i < 25000; i++) {
 
      Long64_t tentry = t->LoadTree(i);
      bvpx->GetEntry(tentry);
 
      for (UInt_t j = 0; j < vpx->size(); ++j) {
 
         h->Fill(vpx->at(j));
 
      }
      if (i && (i%kUPDATE) == 0) {
         if (i == kUPDATE) h->Draw();
         c1->Modified();
         c1->Update();
         if (gSystem->ProcessEvents())
            break;
      }
   }
 
   // Since we passed the address of a local variable we need
   // to remove it.
   t->ResetBranchAddresses();
}
 
 
void hvector()
{
   gBenchmark->Start("hvector");
 
   write();
   read();
 
   gBenchmark->Show("hvector");
}

Author

The ROOT Team

Definition in file hvector.C.