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 Tuesday, March 19, 2024 at 07:21 PM.
Create a histogram for the values we read.
auto myHist = new TH1F("h1","ntuple",100,-4,4);
Open the file containing the tree.
auto myFile = TFile::Open("hsimple.root");
if (!myFile || myFile->IsZombie()) {
return;
}
Create a TTreeReader for the tree, for instance by passing the TTree's name and the TDirectory / TFile it is in.
TTreeReader myReader("ntuple", myFile);
The branch "px" contains floats; access them as myPx.
TTreeReaderValue<Float_t> myPx(myReader, "px");
The branch "py" contains floats, too; access those as myPy.
TTreeReaderValue<Float_t> myPy(myReader, "py");
Loop over all entries of the TTree or TChain.
while (myReader.Next()) {
// Just access the data as if myPx and myPy were iterators (note the '*'
// in front of them):
myHist->Fill(*myPx + *myPy);
}
myHist->Draw();
Info in <TCanvas::MakeDefCanvas>: created default TCanvas with name c1
Draw all canvases
gROOT->GetListOfCanvases()->Draw()