TH1's Y axis

ROOT
1

  1. I’m trying to change the Th1’s Y axis’s labels, but when I’m trying to do it, I found the number of Y axis bin is 1. And I can not change the Y axis labels by SetBinLabel(). What should I do?

  2. I try to draw a TH1F object with option (“hbar”), but the fit result won’t show. How to show it?

  3. The default of (“hbar”) is using the left Y axis as X axis, but I want to use the right Y axis as X axis, how to do that?

Could someone help me, plesa? Thanks a lot~

2

There is an example showing how to use the bar and hbar options here:
$ROOTSYS/tutorials/hist/hbars.C

3

Thanks, but this tutrial doesn’t help.

I want to do the following things:

  1. show the fit curve while using the “hbar” option

  2. show the bars using right Y axis, not left Y axis.

  3. change the TH1’s Y axis’ label.

The tutrial is simple and I still have no idea how to do these.

4

This is not implemented. Fit curves cannot not be shown horizontally.

5 
{
   h = new TH1F("h1","h1",10,-3,3);  
   h->FillRandom("gaus",10000);      
   h->Fit("gaus");  
   TF1 *g=h->GetListOfFunctions()->FindObject("gaus");  
   Double_t x1 = g->GetXmin();
   Double_t x2 = g->GetXmax();
   Double_t dx = (x2-x1)/100;
   Double_t x[100], y[100];
   x[0] = x1;
   y[0] = g->Eval(x[0]); 
   for (int i=1; i<100; i++) {
      x1   = x1+dx;
      x[i] = x1;  
      y[i] = g->Eval(x[i]);
   }
   h->Draw("hbar2");  
   TGraph *gr = new TGraph(100,y,x);
   gr->Draw("L"); 
}
6

Great Idea! Use TGraph to draw the fit result!! It works!
Thanks a lot!

Then how to change the Y axis label? can you help me?

I try:
h->GetYaxis()->SetBinLabel(1,“Tom”); // this one works

h->GetYaxis()->SetBinLabel(2,"Mary");  // this doesn't work

->Error in TAxis::SetBinLabel: Illegal bin number: 2

7

Here is an example:

{
   h = new TH1F("h1","h1",10,-3,3);
   h->FillRandom("gaus",10000);
   h->Fit("gaus");
   for (int bin=1; bin<=10; bin++) {
      h->GetXaxis()->SetBinLabel(bin,Form("Bin #%d",bin));
   }
   TF1 *g=h->GetListOfFunctions()->FindObject("gaus");
   Double_t x1 = g->GetXmin();
   Double_t x2 = g->GetXmax();
   Double_t dx = (x2-x1)/100;
   Double_t x[100], y[100];
   x[0] = x1;
   y[0] = g->Eval(x[0]);
   for (int i=1; i<100; i++) {
      x1   = x1+dx;
      x[i] = x1;
      y[i] = g->Eval(x[i]);
   }
   h->Draw("hbar2");
   TGraph *gr = new TGraph(100,y,x);
   gr->Draw("L");
}

c1.gif696×472 7.49 KB

8

Thanks for your help, you have changed the X axis labels, but not Y axis.

If you change
h->GetXaxis()->SetBinLabel(bin,Form(“Bin #%d”,bin));
to
h->GetYaxis()->SetBinLabel(bin,Form(“Bin #%d”,bin));

it shows:
Error in TAxis::SetBinLabel: Illegal bin number: 2
Error in TAxis::SetBinLabel: Illegal bin number: 3
Error in TAxis::SetBinLabel: Illegal bin number: 4
Error in TAxis::SetBinLabel: Illegal bin number: 5
Error in TAxis::SetBinLabel: Illegal bin number: 6
Error in TAxis::SetBinLabel: Illegal bin number: 7
Error in TAxis::SetBinLabel: Illegal bin number: 8
Error in TAxis::SetBinLabel: Illegal bin number: 9
Error in TAxis::SetBinLabel: Illegal bin number: 10

I want to change the Y axis’s label ( with “hbar” option, it’s X axis now)

9

That’s because for a 1D histogram the Y axis has no bins of course.
try this:

{
   h = new TH1F("h1","h1",10,-3,3);
   h->FillRandom("gaus",10000);
   h->Fit("gaus");
   for (int bin=1; bin<=10; bin++) {
      h->GetXaxis()->SetBinLabel(bin,Form("Bin #%d",bin));
   }
   TF1 *g=h->GetListOfFunctions()->FindObject("gaus");
   Double_t x1 = g->GetXmin();
   Double_t x2 = g->GetXmax();
   Double_t dx = (x2-x1)/100;
   Double_t x[100], y[100];
   x[0] = x1;
   y[0] = g->Eval(x[0]);
   for (int i=1; i<100; i++) {
      x1   = x1+dx;
      x[i] = x1;
      y[i] = g->Eval(x[i]);
   }
   h->GetYaxis()->Set(5,h->GetMinimum(),h->GetMaximum());
   h->GetYaxis()->SetBinLabel(1,"aaa");   
   h->GetYaxis()->SetBinLabel(2,"bbb");   
   h->GetYaxis()->SetBinLabel(3,"bbb");
   h->GetYaxis()->SetBinLabel(4,"bbb");
   h->GetYaxis()->SetBinLabel(5,"ccc");   
   h->Draw("hbar2");   
   TGraph *gr = new TGraph(100,y,x);
   gr->Draw("L");
}