Adding a branch to a tree and saving

Newbie
,
1

Hello; I’m trying to add a branch to a tree from a file.root and then I want to save the file, i wrote the following:

void TreeAdd(){
  TFile *fp = new TFile(FileName.c_str(), "update");
  if (fp->IsZombie()) {
     std::cout << "Error opening file" << std::endl;
     exit(-1);
  }
  TTree *T = (TTree*) fp -> Get(TreePathInFolder.c_str());
  Float_t px;
  Float_t pTest;
  T->SetBranchAddress(OriginalLeaf.c_str(),&px);
  std::string temp = TestBranchName + std::string("/F");
  TBranch *pTestBranch = T->Branch(TestBranchName.c_str(), &pTest, temp.c_str());
  for (Int_t i = 0; i<(nentries); i=i+2) {
    T -> GetEntry(i);
    pTest = px;
    pTestBranch -> Fill();
    }
  T -> Write("",TObject::kOverwrite);
  T -> Print();
  fp -> Save();
  fp -> Close();
}

Now T->Print() does show the modified tree with the added branch but when I reopen the file the tree is not modified, why is this happening?

2

At least:
for (Long64_t i = 0; i < T->GetEntries(); i++) {

3

nentries is T->GetEntries() and I need the for loop to go over only half of the entries. The additional branch gets created so that part of the code should work; the issue is with saving the file

4

I found out that the problem is that instead of adding the new branches to the tree it creates a new tree in the root path of the file that I opened with fp; so the question is: how do I tell my program to add the brances to the existing tree instead of creating a new one?

5

Since you don’t show all the relevant/related code, it’s hard to tell what exactly you are doing. Anyway, one thing to try is to add

  fp->cd();

just before doing T->Write();. Also, I might be wrong but I don’t think fp->Save() exists; in any case it is not needed.

6

Try:

fp->cd("your/folder/with/tree");
TTree *T; gDirectory->GetObject("tree_name", T);
7

Found the solution for the tree situation:

  fp -> cd(FolderNames[SelectedFolder].c_str());
  TTree *T;
  gDirectory->GetObject(TreeNames[0].c_str(), T);
  ...
  T -> Write("", TObject::kOverwrite);

But now I have a new problem, this is the full code:


#define NTrees 4
#define NFolders 4
#define NPlots 2
#define XMin -400.0
#define XMax 400.0
#define YMin -5.0
#define YMax 30000.0

//Change this to change the used folder
#define SelectedFolder 0
#define SelectedTree 0

//Theese are the folder inside the file
std::string FolderNames[NFolders] = {"flashmatchAnaArOnly", "flashmatchAnaXeOnly", "flashmatchAna10ppm"};

//Change this to change the selected leaf
std::string OriginalLeafName = "TrueX";

//Added leafs
std::string TestLeafName = OriginalLeafName + std::string("_test");
std::string FitLeafName = OriginalLeafName + std::string("_fit");

//Change this to change the file from which the tree is loaded
std::string FileName = "../Output/OutAna_500Events_100MeV.root";

//Trees inside each folder
std::string TreeNames[NTrees] = {"FlashMatchTree" ,"LargestFlashTree", "SelectedFlashTree", "CountWaveforms"};

void TreeUpdate(){
  TFile *fp = new TFile(FileName.c_str(), "UPDATE");
  //Check if file is opened
  if (fp->IsZombie()) {
   std::cout << "Error opening file" << std::endl;
   exit(-1);
  }
  std::string TreePathInFolder = std::string("/") + FolderNames[SelectedFolder]+std::string("/")+TreeNames[SelectedTree];
  fp -> cd(FolderNames[SelectedFolder].c_str());
  TTree *T;
  gDirectory->GetObject(TreeNames[0].c_str(), T);

  Float_t px = 0;
  Float_t pTest = 0;
  Float_t pFit = 0;
  //
  //T->SetBranchAddress(OriginalLeafName.c_str(),&px);
  TBranch *OriginalBranch = T -> GetBranch(OriginalLeafName.c_str());
  OriginalBranch->SetAddress(&px);
  OriginalBranch->SetAutoDelete(kTRUE);
  //
  pTest=0;
  pFit=0;
   TBranch *pTestBranch = T->Branch(TestLeafName.c_str(), &pTest, "pcs/F");
   TBranch *pFitBranch = T->Branch(FitLeafName.c_str(), &pFit, "pys/F");
  //
  Long64_t nentries = T->GetEntries();
  //
  Float_t v1[nentries];
  //
  pTest=0;
  pFit=0;
  for (Int_t i = 0; i<nentries; i++) {
    T -> GetEntry(i);
    if(i%2 == 0){
      pTest = px;
      pTestBranch -> Fill();
      }
    else{
      pFit = px;
      pFitBranch -> Fill();
      }
    }
  //
  pTest=0;
  pFit=0;

  T -> Write("", TObject::kOverwrite);
  T -> Print();
  T->Draw(TestLeafName.c_str());
  fp -> Close();
}

I’m trying to take the even and odds entries of my leaf and copy them in two different branches TestLeaf and FitLeaf; this code doesn’t give any error in compilation, the T->Print() shows the added branches with the right number of entries but Draw(TestLeafName.c_str());gives an histogram with an additional column as high as the number of entries; I don’t understand what I’m doing wrong at all
temp_1

temp
temp698×476 11.9 KB

8

All tree branches (i.e., “old” and “new”) must have the same numbers of entries.

9

So my best bet is to make a new tree with only the new branches, right?

10 
  // ...
  for (Int_t i = 0; i<nentries; i++) {
    T -> GetEntry(i);
    if(i%2 == 0){
      pTest = px;
      pTestBranch -> Fill();
      pFit = -9999.;
      pFitBranch -> Fill();
      }
    else{
      pTest = -9999.;
      pTestBranch -> Fill();
      pFit = px;
      pFitBranch -> Fill();
      }
    }
  // ...
  T->Draw(TestLeafName.c_str(), (TestLeafName + " > -9999.").c_str());
  // ...
11

Thank you very much!