MergeFiles.C

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// 'MergeFiles.C'
// Derek Anderson
// 09.25.2020
//
// Merges root files.  Adapted from code
// by Nihar Sahoo.

#include <fstream>
#include <string.h>
#include "TChain.h"
#include "TFile.h"
#include "TH1.h"
#include "TTree.h"
#include "TKey.h"
#include "Riostream.h"



// forward declaration of 'MergeRootFile(TDirectory*, TList*)'
void MergeRootfile(TDirectory *target, TList *sourcelist);



void MergeFiles(const Int_t nFiles=100, const TString filelist= "file.list", const TString outputrootfiles ="test.root") {

  ifstream files;
  //files.open("file2.list");
  files.open(filelist);
  
  char file_stm[800];
  int line=0;

  TList *FileList; 
  TFile *Target; 


  TString filename_output;
  TString chain_;
  Int_t start_num = 0;
  Int_t end_num = 4;
  
  Target = TFile::Open(outputrootfiles, "RECREATE"); 
  FileList = new TList(); 

  while(files.good()) {
            files >> file_stm;

            // quick fix [Derek, 06.02.2017]
            if ((line + 1) > nFiles) {
              cout << "WARNING: Whoah there, tiger! Only need " << nFiles << " files!\n"
                   << "         Moving on to processing files."
                   << endl;
              break;
            }
            
            //___________________
            
            TFile f(file_stm);        
  
            //          Target = TFile::Open( chain_, "RECREATE" ); 

                
            Bool_t fOk = f.IsZombie();
            cout<<"file# "<<line<<"  "<< file_stm<<"  zombi= "<<fOk<<endl;
            
            if(!fOk)
              {
            FileList->Add(TFile::Open(file_stm));
              }
        

            
            if (!files.good()) break;
            line++;
          }
        MergeRootfile( Target, FileList );      


}  // end 'TriggerResolutionStudy_MergeFiles(Int_t, TString, TString)'



void MergeRootfile( TDirectory *target, TList *sourcelist ) {

  //  cout << "Target path: " << target->GetPath() << endl;
  TString path( (char*)strstr( target->GetPath(), ":" ) );
  path.Remove( 0, 2 );

  TFile *first_source = (TFile*)sourcelist->First();
  first_source->cd( path );
  TDirectory *current_sourcedir = gDirectory;
  //gain time, do not add the objects in the list in memory
  Bool_t status = TH1::AddDirectoryStatus();
  TH1::AddDirectory(kFALSE);

  // loop over all keys in this directory
  TChain *globChain = 0;
  TIter nextkey( current_sourcedir->GetListOfKeys() );
  TKey *key, *oldkey=0;
  while ( (key = (TKey*)nextkey())) {

    //keep only the highest cycle number for each key
    if (oldkey && !strcmp(oldkey->GetName(),key->GetName())) continue;

    // read object from first source file
    first_source->cd( path );
    TObject *obj = key->ReadObj();

    if ( obj->IsA()->InheritsFrom( TH1::Class() ) ) {
      // descendant of TH1 -> merge it

      //      cout << "Merging histogram " << obj->GetName() << endl;
      TH1 *h1 = (TH1*)obj;

      // loop over all source files and add the content of the
      // correspondant histogram to the one pointed to by "h1"
      TFile *nextsource = (TFile*)sourcelist->After( first_source );
      while ( nextsource ) {

        // make sure we are at the correct directory level by cd'ing to path
        nextsource->cd( path );
        TKey *key2 = (TKey*)gDirectory->GetListOfKeys()->FindObject(h1->GetName());
        if (key2) {
          TH1 *h2 = (TH1*)key2->ReadObj();
          h1->Add( h2 );
          delete h2;
        }

        nextsource = (TFile*)sourcelist->After( nextsource );
      }
    }
    else if ( obj->IsA()->InheritsFrom( TTree::Class() ) ) {

      // loop over all source files create a chain of Trees "globChain"
      const char* obj_name= obj->GetName();

      globChain = new TChain(obj_name);
      globChain->Add(first_source->GetName());
      TFile *nextsource = (TFile*)sourcelist->After( first_source );
      //      const char* file_name = nextsource->GetName();
      // cout << "file name  " << file_name << endl;
      while ( nextsource ) {

        globChain->Add(nextsource->GetName());
        nextsource = (TFile*)sourcelist->After( nextsource );
      }

    } else if ( obj->IsA()->InheritsFrom( TDirectory::Class() ) ) {
      // it's a subdirectory

      cout << "Found subdirectory " << obj->GetName() << endl;

      // create a new subdir of same name and title in the target file
      target->cd();
      TDirectory *newdir = target->mkdir( obj->GetName(), obj->GetTitle() );

      // newdir is now the starting point of another round of merging
      // newdir still knows its depth within the target file via
      // GetPath(), so we can still figure out where we are in the recursion
      MergeRootfile( newdir, sourcelist );

    } else {

      // object is of no type that we know or can handle
      cout << "Unknown object type, name: "
           << obj->GetName() << " title: " << obj->GetTitle() << endl;
    }

    // now write the merged histogram (which is "in" obj) to the target file
    // note that this will just store obj in the current directory level,
    // which is not persistent until the complete directory itself is stored
    // by "target->Write()" below
    if ( obj ) {
      target->cd();

      if(obj->IsA()->InheritsFrom( TTree::Class() ))
        globChain->Merge(target->GetFile(),0,"keep");
      else
        obj->Write( key->GetName() );
    }

  } // while ( ( TKey *key = (TKey*)nextkey() ) )

  // save modifications to target file
  target->SaveSelf(kTRUE);
  TH1::AddDirectory(status);
}  // end 'MergeRootFiles(TDirectory*, TList*)'

// End ------------------------------------------------------------------------