Hadd

Macro to add histogram files This macro is kept for didactical purposes only: use instead the executable $ROOTSYS/bin/hadd !

This macro will add histograms from a list of root files and write them to a target root file. The target file is newly created and must not be identical to one of the source files. This code is based on the hadd.C example by Rene Brun and Dirk Geppert, which had a problem with directories more than one level deep. The macro from Sven has been enhanced by Anne-Sylvie Nicollerat [email protected] to automatically add Trees (via a chain of trees).

Author: Sven A. Schmidt, [email protected], 13.2.2001
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Thursday, June 17, 2021 at 04:24 PM.

In [1]:
%%cpp -d
#include <string.h>
#include "TChain.h"
#include "TFile.h"
#include "TH1.h"
#include "TTree.h"
#include "TKey.h"
#include "Riostream.h"

TList *FileList;
TFile *Target;

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

A helper function is created:

In [2]:
%%cpp -d
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 the object is a tree, it is stored in globChain...
         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);
}

Prepare the files to me merged

In [3]:
if(gSystem->AccessPathName("hsimple1.root")) {
  gSystem->CopyFile("hsimple.root", "hsimple1.root");
  gSystem->CopyFile("hsimple.root", "hsimple2.root");
}

In an interactive root session, edit the file names Target and FileList, then root > .L hadd.C root > hadd()

In [4]:
Target = TFile::Open( "result.root", "RECREATE" );

FileList = new TList();
FileList->Add( TFile::Open("hsimple1.root") );
FileList->Add( TFile::Open("hsimple2.root") );

MergeRootfile( Target, FileList );