Anne-Sylvie,
See tutorial $ROOTSYS/tutorials/hadd.C
Rene Brun
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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