Reading Multiple root files and plotting one histogram

Newbie
1

HOW to read multiple root files and overlay a particular histogram from all these files into one histogram. I m confused pls help…

2

You can get the histograms you need from the various files and group them into a THStack in order to plot them with axis’ scales automatically computed.
Something like:

auto f1 = new TFile("file1.root");
TH1F *h1 = (TH1F*)f1->Get("hist1");

… etc… for the other files. Then:

auto hs = new THStack();
hs->Add(h1);
hs->Add(h2);

etc … . Then:

hs->Draw();
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3

can i do the same for TEfficiency plots?
and I m using c++

void overlayhist(){

    string fileName = "first.root";

    TFile *f1 = TFile::Open(fileName.c_str());




    string histName1 = "ABC/ABC/eTimingEfficiency";


    TEfficiency* h1 = static_cast<TEfficiency*>(f1->Get(histName1.c_str()));
    TCanvas* c1 = new TCanvas("c1","c1",1000,600);
    c1->cd(1);
    h1->SetTitle("Timing Efficiency");

    h1->Draw();
    gStyle->SetOptStat(0);
    TLegend *leg = new TLegend(0.6,0.7,0.9,0.9);
    leg->AddEntry(h1,"Number: 32");
    leg->Draw();

}

I m using this function to and it successfully plots one file how to add more histograms from other root files as well overlaying it

4

THStack works with histograms. may be you can get the histogram from TEfficiency ?
I guess @moneta can tell.

5

Hi,
TEfficiency will drow TGraphAsymErrors objects. You might use for this instead of THStack TMultiGraph.

Lorenzo

6

can you help me with some dummy code that I have posted above ? To bring more clarity

7

I guess you can retrieve the graphs using GetPaintedGraph.

8

Something like this should work

void overlayEfficiencies(){

   TMultiGraph * mg = new TMultiGraph(); 

// loop  input files 
{
    string fileName = "first.root";
  
    TFile *f1 = TFile::Open(fileName.c_str());




    string histName1 = "ABC/ABC/eTimingEfficiency";


    TEfficiency* h1 = static_cast<TEfficiency*>(f1->Get(histName1.c_str()));
    TCanvas* c1 = new TCanvas("c1","c1",1000,600);
    c1->cd(1);
    h1->SetTitle("Timing Efficiency");

    h1->Draw();
    auto g1 = h1->GetPaintedGraph(); 
    mg->Add(g1);
} 

// end loop 

// draw all the graphs 
mg->Draw();

}

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