{
// Create a directory and a 3D histogram
TDirectory dir1 ("first_dir", "first_dir");
dir1.cd();
TH3D h3d_1 ("h3d", "First dataset", 30, -5, 5, 30, -5, 5, 30, -5, 5);

// fill this histogram with a 3D gaussian
for (int i = 0; i < 100000; i++)
  h3d_1->Fill (gRandom->Gaus(), gRandom->Gaus(), gRandom->Gaus());

// create a xy projection and draw it
h3d_1->Project3D("xy");
h3d_xy->Draw("cont1");

// see the created objects in this directory
dir1.ls();

// Create another directory and 3D histogram
TDirectory dir2 ("second_dir", "second_dir");
dir2.cd();
TH3D h3d_2 ("h3d", "Second dataset", 30, -5, 5, 30, -5, 5, 30, -5, 5);

// fill this histogram with a 3D landau distribution
for (int i = 0; i < 100000; i++)
  h3d_2->Fill (gRandom->Landau(), gRandom->Landau(), gRandom->Landau());

// create a xy projection of this dataset
h3d_2->Project3D("xy");

// see the created objects in this directory
dir2.ls();
}