TTreeReader simplest example.

Read data from hsimple.root (written by hsimple.C)

Author: Anders Eie, 2013
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Sunday, October 02, 2022 at 09:39 AM.

Create a histogram for the values we read.

In [1]:
auto myHist = new TH1F("h1","ntuple",100,-4,4);

Open the file containing the tree.

In [2]:
auto myFile = TFile::Open("hsimple.root");
if (!myFile || myFile->IsZombie()) {

Create a TTreeReader for the tree, for instance by passing the TTree's name and the TDirectory / TFile it is in.

In [3]:
TTreeReader myReader("ntuple", myFile);

The branch "px" contains floats; access them as myPx.

In [4]:
TTreeReaderValue<Float_t> myPx(myReader, "px");

The branch "py" contains floats, too; access those as myPy.

In [5]:
TTreeReaderValue<Float_t> myPy(myReader, "py");

Loop over all entries of the TTree or TChain.

In [6]:
while (myReader.Next()) {
   // Just access the data as if myPx and myPy were iterators (note the '*'
   // in front of them):
   myHist->Fill(*myPx + *myPy);

Info in <TCanvas::MakeDefCanvas>:  created default TCanvas with name c1

Draw all canvases

In [7]: