Re: [ROOT] How to plot two dimensional histogram ?

From: Manoj Jha (Manoj.Jha@cern.ch)
Date: Thu Mar 18 2004 - 15:54:56 MET


Hi Rene,
    Thanks for reply. I am trying to describe my problem in detail. 
Suppose I have two one dimensional histogram, i.e.,

1. One dimensionalm Pt distribution of electron
2.  One dimensional Eta distribution of electron.

Now, I want to plot Eta vs. Pt of the electron. For this purpose, I have 
to create a new two dimensional histogram as
--------------------------------------------------------------------------------------------------------------------
TH2F  *Eta_Pt  = new ("Eta_Pt" , " Eta  Vs. Pt of the electron", 
100,-2.6,2.6,100,0,40);

for (Int_t i=0; i<nentries; i++ )
     Eta_Pt ->Fill(Eta, Pt);
--------------------------------------------------------------------------------------------------------------------

The output of the above script is in the form of scatter plot. That is 
the entries has been plotted as scattered point. Since by default, 2D 
histograms are drawn as scatter plots. Thats why I am getting scatter 
plot.  But I need the plot (Eta_Pt) in the form of  histogram. Please 
let me know if you need any more informations.

Thanks and with regards,
manoj





Rene Brun wrote:

>Hi,
>
>I am not sure to understand correctly your request.
>The example in the attachement will may be give you some hints.
>
>Rene Brun
>
>Manoj Jha wrote:
>  
>
>>Dear Rooters,
>>   I have two one dimensional histograms. I want to plot theses two one
>>dimenasional histograms as one two dimensional histogram.  For this
>>purpose, I used TH2F to create the two dimensional histogram. When using
>>TH2F, I am getting scatter plot. But, I need the two dimensional plot in
>>the form of hitogram instead of scatter plot. Please let me know if you
>>have solution for it.
>>
>>With best wishes,
>>manoj jha
>>    
>>
>>
>
>------------------------------------------------------------------------
>
>void manoj() {
>   TCanvas *c1 = new TCanvas("c1","c1",600,900);
>   c1->Divide(1,2);
>   //method 1
>   c1->cd(1);
>   gPad->SetFrameFillColor(41);
>   gPad->SetTheta(1.97);
>   gPad->SetPhi(2.60);
>   TH2F *h = new TH2F("h","test",30,-3,3,2,0,2);
>   h->SetFillColor(38);
>   h->GetYaxis()->SetNdivisions(2);
>   TRandom r;
>   for (int i=0;i<1000;i++) {
>      h->Fill(1.3*r.Gaus(1,0.8),0.5);
>      h->Fill(1.0*r.Gaus(-1,1),1.5,1.2);
>   } 
>   h->Draw("lego1");
>   
>   //method2
>   c1->cd(2);
>   gPad->SetFrameFillColor(41);
>   gPad->SetTheta(1.97);
>   gPad->SetPhi(2.60);
>   TH2F *h1 = new TH2F("h1","test",30,-3,3,2,0,2);
>   TH2F *h2 = new TH2F("h2","test",30,-3,3,2,0,2);
>   h1->SetFillColor(38);
>   h2->SetFillColor(50);
>   for (int i=0;i<1000;i++) {
>      h1->Fill(1.3*r.Gaus(1,0.8),0.5);
>      h2->Fill(1.0*r.Gaus(-1,1),1.5,1.2);
>   } 
>   THStack *s = new THStack("s","test");
>   s->Add(h1,"lego1");
>   s->Add(h2,"lego1");
>   s->Draw();  
>   s->GetYaxis()->SetNdivisions(2);
>}
>  
>



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