Read in all files in folder and reweight events

I have a directory of files with random names but which can be grouped by their ‘JZ’ number. So for example

And so on, with up to 20 files per JZ tag. I need to reweight the momentum by a different factor for each JZ slice - this isn’t a per event weight, I’ve done those, it’s per slice.

I want to write a C++ macro to do this in root, and basically have no idea where to start. The only way I can think is read in the file names and then do ‘if filename contains 1_*.root …’ then give it the factor to multiply by in each case, that kind of idea, but don’t know where to start to implement that.

I could just paste in all the file names but can’t think how that would help either. If I could get the names then I know what to do:

But I can’t figure out how to give it the inputName of every file in the folder. Its at line 2 where I hit problems, because the JZ%s at the start is predictable but then there are multiple files with the same JZ%s files which all have something different afterwards.

char inputName[200];
TFile f1(inputName,"update");;
    TH1F* h_events = (TH1F*) gDirectory->Get("h_events");
    double evn = h_events->GetEntries();
    double xs;
    double eff;

   if (input.Contains("JZ3_******.root")){ xs = 1;  eff = 1; } 
   if(input.Contains("JZ3_******.root")){xs=; eff =1;}
   double reweight = xs*eff/evn;

    double EvweightLC;   double new_weightLC;
    double EvweightEM;   double new_weightEM;

    TTree *LC = (TTree*)f1.Get("AntiKt4LCTopoJets");
    TTree *EM = (TTree*)f1.Get("AntiKt4EMTopoJets");

    TBranch* newBranchLC = LC->Branch("new_EventWeight",&new_weightLC, "new_weightLC/D");
    TBranch* newBranchEM = EM->Branch("new_EventWeight",&new_weightEM, "new_weightEM/D");


    int entriesLC = LC->GetEntries();
    int entriesEM = EM->GetEntries();

    for (int i=0; i<entriesLC; i++) {
      new_weightLC = EvweightLC*reweight;

      for (int i=0; i<entriesEM; i++) {
        new_weightEM = EvweightEM*reweight;


Sorry, I think I haven’t explained that well at all! I’d really appreciate any help and happy to clarify the confusing bits. :slight_smile: Thanks!

I do not know if that’s what you are looking for but TString provides all the tools to compare character strings.

This topic was automatically closed 14 days after the last reply. New replies are no longer allowed.