copyEvents.C

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////////////////////////////////////////////////////////////////////////////////
//                                                                            //
// copyEvents.C                                                               //
//                                                                            //
// An example macro how to copy only a part of events from a source file      //
//                                                                            //
////////////////////////////////////////////////////////////////////////////////
 
int copyEvents(TString inputFilePath, TString outputFilePath, Int_t nStartEvent = 10000, Int_t nEvents = 100)
{
    if (inputFilePath == "") {
        cout << "ERROR: Input file path was not specified" << endl;
        return -1;
    }
    gSystem->ExpandPathName(inputFilePath);
 
    if (outputFilePath == "") {
        cout << "ERROR: Output file path was not specified" << endl;
        return -2;
    }
    gSystem->ExpandPathName(outputFilePath);
 
    TFile* inputFile = new TFile(inputFilePath.Data());
    if (!inputFile) {
        cout << "ERROR: Input file was not opened: " << inputFilePath << endl;
        return -3;
    }
 
    TFile* outputFile = new TFile(outputFilePath.Data(), "RECREATE");
    if (!outputFile) {
        cout << "ERROR: Output file was not opened: " << outputFilePath << endl;
        return -4;
    }
 
    // loop on all entries to find all trees (or FairRootManager::GetTreeName() can be used)
    TTree* inputTree = (TTree*)inputFile->Get(FairRootManager::GetTreeName());
    if (!inputTree) {
        cout << "ERROR: Input tree was not obtained: " << FairRootManager::GetTreeName() << endl;
        return -5;
    }
    TTree* outputTree = inputTree->CloneTree(0);
    inputTree->CopyAddresses(outputTree);
 
    const auto nentries = inputTree->GetEntries();
    if (nEvents == 0)
        nEvents = nentries - nStartEvent;
    else if ((nStartEvent + nEvents) > nentries)
        nEvents = nentries - nStartEvent;
    cout << "Tree Name: " << FairRootManager::GetTreeName() << ", event count = " << nEvents << endl;
 
    for (int i = nStartEvent; i < nStartEvent + nEvents; i++) {
        inputTree->GetEntry(i);
        outputTree->Fill();
    }
    outputTree->Write();
 
    delete inputFile;
    delete outputFile;
    return 0;
}