Offset in height for a TH2

[juliangb]

Hello,

I want to draw one 2D histogram that doesn’t start at 0 when the bin is empty, but at a fixed height on the z axis, let’s say z0, so that the space between 0 an z0 in the z axis is empty.

The reason I want to do this is that I want to draw some (let’s say two) 2D histograms in the same pad, separated in the z axis by a given value.

I thought this could be the best way to do so, and then overlapping the histograms with this offset but I couldn’t even find a way to set this offset for one histogram.

To be short, I need a command like “myhist->StartFrom(z0)”

Apologies in advance if this is too basic, I would appreatiate your help on this problem.

ROOT Version: 6.14/04
Platform: Ubuntu

[Wile_E_Coyote]

myhist->SetMinimum(z0);

[juliangb]

This is what I thought at first, but it only hides the bins with height <z0, which re-appear when I unzoom. I need that the histogram starts filling from z0 so that when I unzoom there’s a blank space between 0 and z0.

Thanks for your support,

Julian.

[couet]

The following code will do the vertical shift of a TH2:

void addconstth2( TH2F* h, float z) {
   int nbinx = h->GetNbinsX();
   int nbiny = h->GetNbinsY();
   for (int i=1; i<=nbinx; i++) {
      for (int j=1; j<=nbiny; j++) {
         h->SetBinContent(i,j,h->GetBinContent(i,j)+z);
      }
   }
}

[juliangb]

This code is really helphul, thanks! But it’s still not what I have in mind, sorry if I wasn’t clear on that.

The code does boost the hight of every element of the histogram to the desired z0, but it’s still visible from 0 to z0. I’m lookin forward to get something like this:

where the white bins should be nothing but blank space.

(sorry if I took a while to respond, but I was trying to solve it myself with your code).

Thanks again for the help.

[couet]

I do not see an easy way how to make this space completely empty …
Using THStack you will get something similar to the picture you sent. Ie: not empty
may be a 3D histogram draw with option box can provide something more useful for you … not sure … I do not have ideas right now.

[couet]

Using THSack and a transparent level I can do the attached picture. But that does not really work as the histogram at the bottom is on partially drawn.

[juliangb]

Yes, I usted THStack to make the figure above, I used the blank bins to make myself more clear, but later I could make them transparent, all with help of your code.

But, as you pointed out yourself, all histograms in the bottom will be incomplete because they have a transparent histogram on top of if.

I think this is good enough though, so thanks for your help!

But I’ll keep this open in case that someone comes up with the solution to this problem.

[couet]

The macro producing the previous plot is:

TH2F *spaceabove(TH2F *h, float s, TString ht, int c) {
   int nbinx = h->GetNbinsX();
   int nbiny = h->GetNbinsY();
   float x1 = h->GetXaxis()->GetXmin();
   float x2 = h->GetXaxis()->GetXmax();
   float y1 = h->GetYaxis()->GetXmin();
   float y2 = h->GetYaxis()->GetXmax();

   auto hs = new TH2F(ht.Data(), ht.Data(),nbinx, x1, x2, nbiny, y1 , y2);

   for (int i=1; i<=nbinx; i++) {
      for (int j=1; j<=nbiny; j++) {
         hs->SetBinContent(i,j,s-h->GetBinContent(i,j));
      }
   }
   hs->SetFillColor(c);
   return hs;
}

void flyinglegoplots() {

   Int_t ci = 1756;
   auto *c = new TColor(ci, 1., 0., 0.3, "", 0.);
   Int_t dark   = TColor::GetColorDark(ci);
   auto *cd = gROOT->GetColor(dark);
   cd->SetAlpha(0.);
printf("dark = %d\n",dark);

   THStack *a = new THStack("a","Stacked 2D histograms");

   TF2 *f1 = new TF2("f1", "xygaus + xygaus(5) + xylandau(10)",-4,4,-4,4);
   Double_t params[] = {130,-1.4,1.8,1.5,1, 150,2,0.5,-2,0.5, 3600,-2,0.7,-3,0.3};
   f1->SetParameters(params);

   TH2F *h2sta = new TH2F("h2sta","h2sta",20,-4,4,20,-4,4);
   h2sta->SetFillColor(38);
   h2sta->FillRandom("f1",4000);

   TF2 *f2 = new TF2("f2","xygaus + xygaus(5)",-4,4,-4,4);
   Double_t params2[] = {100,-1.4,1.9,1.1,2, 80,2,0.7,-2,0.5};
   f2->SetParameters(params2);
   TH2F *h2stb = new TH2F("h2stb","h2stb",20,-4,4,20,-4,4);
   h2stb->SetFillColor(46);
   h2stb->FillRandom("f2",3000);

   a->Add(h2sta);
   a->Add(spaceabove(h2sta, 50, "hs1",ci));
   a->Add(h2stb);


   a->Draw("lego3");
}

[couet]

An other approach:

{
   gStyle->SetOptStat(0);
   gStyle->SetHistTopMargin(0);

   auto f1 = new TF2("f1", "xygaus + xygaus(5) + xylandau(10)",-4,4,-4,4);
   Double_t params[] = {130,-1.4,1.8,1.5,1, 150,2,0.5,-2,0.5, 3600,-2,0.7,-3,0.3};
   f1->SetParameters(params);
   auto h2sta = new TH2F("h2sta","",20,-4,4,20,-4,4);
   h2sta->SetFillColor(38);
   h2sta->FillRandom("f1",4000);

   auto f2 = new TF2("f2","xygaus + xygaus(5)",-4,4,-4,4);
   Double_t params2[] = {100,-1.4,1.9,1.1,2, 80,2,0.7,-2,0.5};
   f2->SetParameters(params2);
   auto *h2stb = new TH2F("h2stb","",20,-4,4,20,-4,4);
   h2stb->SetFillColor(46);
   h2stb->FillRandom("f2",3000);

   auto C = new TCanvas();

   double ph = 0.5;
   double p2y = 0.22;

   double max = h2stb->GetMaximum()*1.5;

   h2sta->SetMaximum(max);
   h2stb->SetMaximum(max);

   C->cd();
   auto *pad1 = new TPad("pad1","",0,0,1,ph);
   pad1->SetFillStyle(4000);
   pad1->Draw(); pad1->cd();   h2sta->Draw("lego1 fb  ");

   C->cd();
   auto *pad2 = new TPad("pad2","",0,p2y,1,p2y+ph);
   pad2->SetFillStyle(4000);
   h2stb->GetXaxis()->SetLabelSize(0); h2stb->GetYaxis()->SetLabelSize(0);
   h2stb->GetXaxis()->SetTickSize(0);  h2stb->GetYaxis()->SetTickSize(0);
   pad2->Draw(); pad2->cd();   h2stb->Draw("lego1 fb  ");

}

[juliangb]

Last one does the trick, thanks!