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Reference Guide
copytree.C File Reference

Detailed Description

View in nbviewer Open in SWAN Copy a subset of a Tree to a new Tree

The input file has been generated by the program in $ROOTSYS/test/Event with Event 1000 1 1 1.

// Load the library at macro parsing time: we need this to use its content in the code
R__LOAD_LIBRARY($ROOTSYS/test/libEvent.so)
void copytree()
{
TString dir = "$ROOTSYS/test/Event.root";
const auto filename = gSystem->AccessPathName(dir) ? "./Event.root" : "$ROOTSYS/test/Event.root";
TFile oldfile(filename);
TTree *oldtree;
oldfile.GetObject("T", oldtree);
// Deactivate all branches
oldtree->SetBranchStatus("*", 0);
// Activate only four of them
for (auto activeBranchName : {"event", "fNtrack", "fNseg", "fH"})
oldtree->SetBranchStatus(activeBranchName, 1);
// Create a new file + a clone of old tree in new file
TFile newfile("small.root", "recreate");
auto newtree = oldtree->CloneTree();
newtree->Print();
newfile.Write();
}
Author
Rene Brun

Definition in file copytree.C.

TTree::CloneTree
virtual TTree * CloneTree(Long64_t nentries=-1, Option_t *option="")
Create a clone of this tree and copy nentries.
Definition: TTree.cxx:3089
TTree
A TTree represents a columnar dataset.
Definition: TTree.h:79
TTree::Print
virtual void Print(Option_t *option="") const
Print a summary of the tree contents.
Definition: TTree.cxx:7095
TString
Basic string class.
Definition: TString.h:136
TSystem::AccessPathName
virtual Bool_t AccessPathName(const char *path, EAccessMode mode=kFileExists)
Returns FALSE if one can access a file using the specified access mode.
Definition: TSystem.cxx:1294
test
Definition: test.py:1
TSystem::ExpandPathName
virtual Bool_t ExpandPathName(TString &path)
Expand a pathname getting rid of special shell characters like ~.
Definition: TSystem.cxx:1272
void
typedef void((*Func_t)())
TFile
A ROOT file is a suite of consecutive data records (TKey instances) with a well defined format.
Definition: TFile.h:54
gSystem
R__EXTERN TSystem * gSystem
Definition: TSystem.h:559
TTree::SetBranchStatus
virtual void SetBranchStatus(const char *bname, Bool_t status=1, UInt_t *found=0)
Set branch status to Process or DoNotProcess.
Definition: TTree.cxx:8359
R__LOAD_LIBRARY
#define R__LOAD_LIBRARY(LIBRARY)
Definition: Rtypes.h:472