Create a TTree filled with double, vector<double>, and vector<vector<double> > #askROOT

ROOT tutorial #2

Download the C codes and run the following commands:

$ alias rot='root -l -b -q'
$ rot create_vector_vars.C+
$ rot read_vector_vars.C+

Tested in ROOT 6.06/00

create_vector_vars.C

#include "TFile.h"
#include "TTree.h"
#include "TRandom.h"
#include "TSystem.h"
#include "TInterpreter.h"

#include <vector>

void create_vector_vars() {

    gInterpreter->GenerateDictionary("vector<vector<double> >","vector");

    TFile * f1 = TFile::Open("giallo.root", "RECREATE");
    gRandom->SetSeed(1);

    TTree * t1 = new TTree("tree1", "tree1");
    double var1;
    std::vector<double> var2;
    std::vector<std::vector<double> > var3;

    t1->Branch("var1", &var1);
    t1->Branch("var2", &var2);
    t1->Branch("var3", &var3);

    for (int i=0; i<100; i++) {
        var1 = gRandom->Rndm();

        for (int j=0; j<10; j++) {
            var2.push_back(gRandom->Rndm());
            var3.push_back(std::vector<double>());

            for (int k=0; k<10; k++) {
                var3.back().push_back(gRandom->Rndm());
            }
        }

        t1->Fill();

        var2.clear();
        var3.clear();
    }

    t1->Write();
    f1->Close();

}

read_vector_vars.C

#include "TFile.h"
#include "TTree.h"
#include "TRandom.h"
#include "TSystem.h"

#include <vector>
#include <iostream>

void read_vector_vars() {

    TFile * f1 = TFile::Open("giallo.root", "READ");

    TTree * t1 = (TTree *) f1->Get("tree1");
    double var1;
    std::vector<double> * var2 = 0;
    std::vector<std::vector<double> > * var3 = 0;

    t1->SetBranchAddress("var1", &var1);
    t1->SetBranchAddress("var2", &var2);
    t1->SetBranchAddress("var3", &var3);

    for (int i=0; i<t1->GetEntries(); ++i) {
        t1->GetEntry(i);

        std::cout << "evt " << i << " var1: " << var1 << std::endl;
    }

    for (int i=0; i<t1->GetEntries(); ++i) {
        t1->GetEntry(i);

        for (int j=0; j<var2->size(); ++j) {
            std::cout << "evt " << i << " var2[" << j << "]: " << var2->at(j) << std::endl;
        }
    }

    for (int i=0; i<t1->GetEntries(); ++i) {
        t1->GetEntry(i);

        for (int j=0; j<var3->size(); ++j) {
            for (int k=0; k<var3->at(j).size(); ++k) {
                std::cout << "evt " << i << " var3[" << j << "][" << k << "]: " << var3->at(j).at(k) << std::endl;
            }
        }
    }


    f1->Close();

}