Manipulating histogram that has drawn the axis

ROOT
1

Hi all,

I have several functions that do return a pointer to the histogram that draw the axis in the current canvas, in order to modify the axis properties.

What I want to do works successfully when I return THStack::GetHistogram() or TGraph::GetHistogram() but not in the example below:

#include "TH1.h"
#include "TCanvas.h"
#include "TROOT.h"
#include "TStyle.h"

#include <vector>

bool HistScaledGT ( TH1* h1, TH1* h2 )
{ 
	return (h1->GetMaximum()/h1->Integral()) < (h2->GetMaximum()/h2->Integral());
}

template <class T>
T* DrawNormHists( const std::vector<T*> &h_vec )
{
	
	typename std::vector<T*>::const_iterator it, it2;
	
	it = max_element( h_vec.begin(), h_vec.end(), HistScaledGT );
	
	if( it != h_vec.end() )
	{ 
		(*it)->DrawNormalized("hist"); // Drawn with axis
		for( it2 = h_vec.begin() ; it2 != h_vec.end() ; it2++ )
			if( (*it2)->Integral() > 0 ) (*it2)->DrawNormalized("hist same A");
	}
	
	return *it; // Return histogram used to build axis
	
}


int main()
{
	gROOT->SetStyle("Plain");
	// gStyle->SetOptTitle(0);
	gStyle->SetOptStat(0);
	
	std::vector<TH1F*> h_vec;
	
	h_vec.push_back( new TH1F("h1", "h1", 50, -10, 10) );
	h_vec.back()->FillRandom("gaus");
	h_vec.push_back( new TH1F("h2", "h2", 50, -10, 10) );
	h_vec.back()->FillRandom("landau");
	h_vec.push_back( new TH1F("h3", "h3", 50, -10, 10) );
	h_vec.back()->FillRandom("expo"); // This will be the maximum
	h_vec.back()->SetTitle("InitTitle");
	
	TCanvas *c = new TCanvas("tmp","", 600, 600);
	
	TH1* f = DrawNormHists( h_vec );
	
	// These don't work. Why ?
	f->SetTitle("A title");
	f->GetXaxis()->SetTitle("Hello");

	c->Modified();
	c->Update();
	c->ForceUpdate(); // Even after this
	
	c->Print(".png");
	
	return 0;

}

What am I doing wrong ?

Is there another option to draw a bunch of normalized histograms so that they plot nicely. I could fill a THStack with scaled histograms but I’d rather avoid duplicating the histograms.

Is there any reason why THStack has no DrawNormalized() member function?

I am using ROOT 5.18/00 trunk@21744 on MacOS X. Is it time to upgrade ?

Thanks in advance for your help.

Karolos

2

Your macro gives me errors. Can you send something I can run in ROOT ?
In principal what you are doing is correct. Though you do not need the option “A” when you plot histogram using the option “SAME”… But should not make any difference.

3

Hi Olivier,

Thanks for your reply.

I removed the template and renamed the main().

The attached code runs fine on my version of ROOT 5.18/00 trunk@21744 on MacOS X.

root -l tmp_root.C

It produces the results but it doesn’t allow me to change the title (or the axis title, which is my main need) of the histogram that draw the axes.

Indeed, the A is a leftover from iterations in the code but it doesn’t hurt.

Karolos
tmp_root.C (1.4 KB)

4

Hi Karolos,

Still something wrong with your macro:

pb-d-128-141-132-114:roottest couet$ root -l tmp_root.C
root [0] 
Processing tmp_root.C...
Error: Function comp(*result,*first) is not defined in current scope  algo.h:2341:
*** Interpreter error recovered ***
root [1]
5

Olivier,

I’m sorry. I checked this code on several machines including LXPLUS and it worked fine.

In any case, I did remove the call to the STL max_element, which is not the purpose of my post.

I again checked on the platforms I have available. I hope it works for you too now.

Thanks,

Karolos
tmp_root2.C (1.64 KB)

6

It is ok now. I can run your macro. I’ll let you know.

7

Great. Thank you.

8

I do not understand yet. The only way I found to make it work right now is to set the h3’s attributes before calling DrawNormHists. Is that acceptable for you ?

9

The following very stupid one is working:

TH1F* DrawHists(TH1F *h1, TH1F *h2, TH1F *h3)
{
   TH1F *h = h3;
   h3->Draw();
   h2->Draw("same");
   h1->Draw("same");
   return h;
}


tmp_root3()
{
   TH1F *h1 = new TH1F("h1", "h1", 50, -10, 10);
   h1->FillRandom("gaus");

   TH1F *h2 = new TH1F("h2", "h2", 50, -10, 10);
   h2->FillRandom("landau");

   TH1F *h3 = new TH1F("h3", "h3", 50, -10, 10);
   h3->FillRandom("expo");
   

   TCanvas *c = new TCanvas("tmp","", 600, 600);

   TH1F* f = DrawHists( h1, h2, h3 );
   f->SetTitle("A title");
   f->GetXaxis()->SetTitle("Hello");
}
10

Thank you Olivier.

To search for the histogram that is going to be plotted defeats the purpose of a single function returning the histogram that is of importance. Applying the axis title to all the histograms beforehand is also not optimal. But I can live with that.

The strange thing is that this example works if TH1s had been TGraphs inside a TMultiGraph, for which I return TMultiGraph::GetHistogram(). Perhaps this is a hint to the solution ?

BTW is there any reason why there’s no THStack::DrawNormalized() ? Since THStack::GetHistogram() works just fine too.

In any case, it’s not really a critical issue. It would just be nice that things work as expected (unless I’m doing something weird).

Thanks,

Karolos

11

I suspect that some how the wrong histogram is returned in you case as it works correctly in the last example I sent you … But I must Admit I have not found what is wrong in your macro.

12

Indeed, my code works fine when using TH1::Draw().

Now that I think of it, normalized drawing should derive a new histogram not to erase the old. So I need to get the pointer to the DrawNormalized() histogram.

Thanks Olivier for investigating this.

Solution yielded using

TH1F *retval;
retval = (TH1F*) (*it)->DrawNormalized("hist"); // Drawn with axis

return retval;

in appropriate places.

Karolos

[quote=“couet”]The following very stupid one is working:

[code]
TH1F* DrawHists(TH1F *h1, TH1F *h2, TH1F *h3)
{
TH1F *h = h3;
h3->Draw();
h2->Draw(“same”);
h1->Draw(“same”);
return h;
}

tmp_root3()
{
TH1F *h1 = new TH1F(“h1”, “h1”, 50, -10, 10);
h1->FillRandom(“gaus”);

TH1F *h2 = new TH1F(“h2”, “h2”, 50, -10, 10);
h2->FillRandom(“landau”);

TH1F *h3 = new TH1F(“h3”, “h3”, 50, -10, 10);
h3->FillRandom(“expo”);

TCanvas *c = new TCanvas(“tmp”,"", 600, 600);

TH1F* f = DrawHists( h1, h2, h3 );
f->SetTitle(“A title”);
f->GetXaxis()->SetTitle(“Hello”);
}
[/code][/quote]

13

Yes, I think that’s the way you should investigate.