Root macro to retrieve and copy in a csv file the number of photo-electrons from a root file

SarahBlind · November 21, 2023, 11:09am

Dear Root users,

I am using GATE (an open source software dedicated to digital simulations in medical imaging and radiotherapy) to analyze some radio physical quantities (photo-electrons for example) after an X-rays irradiation simulation. I’m using root 6.28/08 on Ubuntu 20.04.6 LTS.

My GATE simulations give rise to .root files in which I can found the number of photo-electrons produced.

I know how to recover this number “by hand” in the T Browser :

or through the root prompt :

But I would like to make a root macro that goes through each root files, recover and copy the number of photo-electrons produced for each root file into an ods or csv file.

I know how to open my root file :

std::unique_ptr myFile( TFile::Open(“phaseSpaceCluster_IN.root”) );

but I can’t manage to find how to retrieve the number of photo-electrons…
In other words, how can I implement the root prompt command line

PhaseSpace->Draw(“Ekine”,“CreatorProcess=="PhotoElectric"”)

into a root macro ? Does anyone have any tips to help me?

Many thanks for your help!

Sarah

dastudillo · November 21, 2023, 12:39pm

You can read the tree with an RDataFrame and use Filter() and Count():

void test() {
  ROOT::RDataFrame d("PhaseSpace", "phaseSpaceCluster_IN.root");
  auto n = d.Filter("CreatorProcess==\"PhotoElectric\"").Count();
  cout << *n << endl;
}

(save as test.C)
Note the *n, since Count() returns a pointer.