This macro illustrates how to create a hierarchy of directories in a Root file. Ten directories called plane0, plane1, ..., plane9 are created. Each plane directory contains 200 histograms. Note that the macro deletes the TFile object at the end! Connect the file again in read mode:

Root [0] TFile top("top.root");

The hierarchy can be browsed by the Root browser as shown below

Root  TBrowser b;

Click on the left pane on one of the plane directories. This shows the list of all histograms in this directory. Double click on one histogram to draw it (left mouse button). Select different options with the right mouse button. Instead of using the browser, you can also do:

Root > tof->cd();
  Root > plane3->cd();
  Root > h3_90N->Draw();

Author: Rene Brun
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Thursday, June 17, 2021 at 04:23 PM.

Create a new root file

In [1]:
TFile *top = new TFile("top.root","recreate");

Create a subdirectory "tof" in this file

In [2]:
TDirectory *cdtof = top->mkdir("tof");
cdtof->cd();    // make the "tof" directory the current directory

Create a new subdirectory for each plane

In [3]:
const Int_t nplanes = 10;
const Int_t ncounters = 100;
char dirname[50];
char hname[20];
char htitle[80];
Int_t i,j,k;
TDirectory *cdplane[nplanes];
TH1F *hn[nplanes][ncounters];
TH1F *hs[nplanes][ncounters];
for (i=0;i<nplanes;i++) {
   cdplane[i] = cdtof->mkdir(dirname);
   // create counter histograms
   for (j=0;j<ncounters;j++) {
      sprintf(htitle,"hist for counter:%d in plane:%d North",j,i);
      hn[i][j] = new TH1F(hname,htitle,100,0,100);
      sprintf(htitle,"hist for counter:%d in plane:%d South",j,i);
      hs[i][j] = new TH1F(hname,htitle,100,0,100);
   cdtof->cd();    // change current directory to top

Fill histograms

In [4]:
TRandom r;
for (i=0;i<nplanes;i++) {
   for (j=0;j<ncounters;j++) {
      for (k=0;k<100;k++) {

Save histogram hierarchy in the file

In [5]:
delete top;