Hi, You can try the following macro. I forgot how I got it. It will chain your "Global" root-trees to a chain named globChain. //---------------------------------------------------------- TChain *globChain = new TChain("Global"); TString fNameList = TString("my-files.list"); cout << ">>> Load Chain from file: " << fNameList << endl; ifstream fList((char*)fNameList); if (!fList) { cout << "!!! Can't open file " << fNameList << endl; return; } char lineFromFile[255]; while(fList.getline(lineFromFile, 250)) { TString fileName = lineFromFile; fileName = "/exp/D0/vuanh/D0Rawdata/" + fileName; if(globChain->Add((char*)fileName)) cout << ">> File '" << fileName << "' has been loaded" << endl; else cout << ">> Can't load file '" << fileName << "'" << endl; } cout << ">> Total number of entries: " << globChain->GetEntries() << endl; fList.close(); //---------------------------------------------------------- You need to provide your file list, something like this essai0.root essai1.root essai2.root with a blank line at the end so the macro can read them all. Now you can work with your "globChain" as it were your "Global" tree. Tuan On Mon, 3 Jun 2002, Anne-Sylvie Nicollerat wrote: > Hello, > > I would like to know if it is possible to combine root files. > > I am now running on big sets of data and to go faster, I divided the > data set in 4 different subsets. I am now running root parallely on each > of the subsets, writing 4 different .root files. > In the end, I would like to combine the histograms of the 4 different > root files. A way I found was to open all the files and then add the > histograms. > (eg: > f10 = new TFile("essai0.root"); > f11 = new TFile("essai1.root"); > ..... > TH1D *a1=(TH1D*) f10->Get("z0100"); > TH1D *a2=(TH1D*) f10->Get("z0101"); > > TH1D *b1=(TH1D*) f11->Get("z0100"); > TH1D *b2=(TH1D*) f11->Get("z0101"); > > .... > a1->Add(b1); > a2->Add(b2); > .....) > > I was wondering if there was a possibility to do it in a more > staightforward way (that means without needing to ask root to add > separately all the histograms I am interested in). > I saw that there was an Add and an Append method for a root files but > somehow I didn't find out how it worked. > > Thanks a lot for your help > > cheers > > Anne-Sylvie > >
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