Get distinct entries from tbranch

ROOT
1

Hi,

I am looking for a nice way to get all different values from branches which contain either ints or strings.

Other branches in the tree contain a continuous range of values, but some contain very few different values which I would like to retrieve to enable a selection by those values.

The closest analogy that comes to my mind is a “select distinct” in an oracle query.

Any suggestions apart from manually looping over all entries of the tree?

Cheers

Erik

2

if your Tree has been created from an object, you can get some inspiration from the example below where Event.root is the file generated by running
Event 100 1 99 1
in $ROOTSYS/test (run make in this dir)

[code]void selectb() {
//open a tree and print the leaf names with integers or strings

TFile f(“Event.root”);
TTree T = (TTree)f.Get(“T”);
TIter next(T->GetListOfLeaves());
TLeafElement leaf;
while ((leaf = (TLeafElement)next())) {
TString typeName = leaf->GetTypeName();
printf(“leaf = %s, typeName = %s\n”,leaf->GetName(),typeName.Data());
if (typeName == “Int_t”) {
printf(" found leaf: %s with integer type\n",leaf->GetName());
} else if (typeName == “Char_t”) {
printf(" found leaf: %s with string type\n",leaf->GetName());
}
}
}
[/code]

Rene

3

Hi Rene,

thanks for the answer. If I read the code correctly however, this is not what I intended to do.

The example below maybe illustrates the problem. What I would like to get is the range [0:9] for i and [0:4] for j.

Cheers,

Erik

void branchrange()
{
  TFile *f = new TFile("test.root","RECREATE");
  TTree *tree = new TTree("tree","My Tree");
  Int_t i, j;
  Double_t x,y;
  tree->Branch("i",&i,"i/I");
  tree->Branch("j",&j,"j/I");
  tree->Branch("x",&x,"x/D");
  tree->Branch("y",&y,"y/D");
  
  for(int k = 0; k < 10000; ++k) {
    x = gRandom->Gaus();
    y = gRandom->Gaus();
    i = k/1000;
    j = k/2000;
    tree->Fill();
  }

  tree->Write();
    
  for(int k = 0; k < tree->GetEntriesFast(); ++k) {
    tree->GetEntry(k);
    std::cout << i << ' ' << j << ' ' << x << ' ' << y << std::endl;
  }
  
}
4

Your explanations are still quite unclear. May be have a look at the following changes

Rene

[code]void branchrange()
{
TFile *f = new TFile(“test.root”,“RECREATE”);
TTree *tree = new TTree(“tree”,“My Tree”);
Int_t i, j;
Double_t x,y;
TBranch * bi = tree->Branch(“i”,&i,“i/I”);
TBranch * bj = tree->Branch(“j”,&j,“j/I”);
TBranch * bx = tree->Branch(“x”,&x,“x/D”);
TBranch * by = tree->Branch(“y”,&y,“y/D”);

for(int k = 0; k < 10000; ++k) {
x = gRandom->Gaus();
y = gRandom->Gaus();
i = k/1000;
j = k/2000;
tree->Fill();
}

tree->Write();

for(int k = 0; k < tree->GetEntriesFast(); ++k) {
bi->GetEntry(k);
if (i !=3) continue; //do not read anything else
bj->GetEntry(k);
if (j != 1) continue;
tree->GetEntry(k); //read everything else otherwise
std::cout << i << ’ ’ << j << ’ ’ << x << ’ ’ << y << std::endl;
}

}
[/code]

5

Hi Rene,

trying to clarify (hopefully) more.

The tree is the output from a different script and prior to doing any full analysis on it, I would like to get the range of values from some of the branches.

The code example should illustrate the data structure, namely that I have a very limited number of different values in branches i and j which I would like to retrieve.

If I then want to exclude or include certain values of either variable, the code changes you provided do what I want, but I would like to get the different values beforehand if possible.

Maybe there is no truly simple method and I can just disable all other branches prior to looping over the tree, to minimize the amount of data to be read.

Any other suggestion?

Thanks,

Erik

6

Simply make a histogram of your variables like I and J and in the histo select the non-empty bins.

Rene

7

Hi Rene,

now thats indeed a good and simple solution. I did not think of this.

Thanks