How to set different line color in TTree::Draw()

[ZhuKun]

The code in $ROOTSYS/tutorials/tree/tree0.C

tree->Draw("a.e");  //energy of det a
tree->Draw("a.e","3*(-.2<b.e && b.e<.2)","same");

Question:
Now , we have two histograms in the same pad.But,how to let the different line with different color in code?

ROOT Version: ROOT 6.14
Platform: Ubuntu
Compiler: default

[couet]

tree->Draw("a.e");  //energy of det a
tree->Draw("a.e","3*(-.2<b.e && b.e<.2)","same");
htemp->SetLineColor(kRed);

[ZhuKun]

@couet

htemp->SetLineColor(kRed);

There is no “themp” pointer in the code .And although you use the code “tree->SetLineColor(kRed);”,we just change one line.

[FoxWise]

I usually do:

tree->Draw("a.e");  //energy of det a
tree->Draw("a.e>>histo","3*(-.2<b.e && b.e<.2)","same");
TH1F* h = (TH1F*) gROOT->FindObject("histo");
h->SetLineColor(2);

[couet]

It works for me:

root [1] ntuple->Draw("px") 
Info in <TCanvas::MakeDefCanvas>:  created default TCanvas with name c1
root [2] htemp->SetLineColor(kRed)

[ZhuKun]

Thanks a lot! I tried and it works.

[ZhuKun]

Thanks a lot!But the htemp is not declared in the code,Maybe the code is different.

[couet]

In a macro:

   nt->Draw("px"); 
   TH1F *htemp = (TH1F *)gPad->GetPrimitive("htemp");
   htemp->SetLineColor(kRed);

[ZhuKun]

I tried and it works in only one line.How can we change the other lines’ color in this way?Why can we find an object “themp” in the code ?

[couet]

@ZhuKun

it works in only one line

what do you mean ? can you post an example ?

[ZhuKun]

As is shown in fifth reply,one line is green and the other is red.

[couet]

ok, so what is wrong ? the screen dump is correct according to the commands you displayed on the left.

[dastudillo]

If we have

 tree->Draw("something");
 tree->Draw("sometihng_else","same");

doing .ls shows that both histos are called htemp, and gPad->GetPrimitive("htemp") only retrieves one of the histos (the first one); the question is how to get the second one in this case (when the Draw line didn’t explicitly create named histos).

[couet]

root [1] ntuple->Draw("px"); htemp->SetName("h1"); h1->SetLineColor(2);
root [2] ntuple->Draw("py","","same"); htemp->SetLineColor(3);

[ZhuKun]

But the identifier ‘h1’ is not defined before.

[couet]

{
   auto f = new TFile("hsimple.root");
   TNtuple *n = (TNtuple*)f->Get("ntuple");
   n->Draw("px","","nodraw");
   TH1F* h1 = (TH1F*) gROOT->FindObject("htemp");
   h1->SetName("h1"); h1->SetLineColor(2);
   h1->Draw();
   ntuple->Draw("py","","same");
   TH1F* h2 = (TH1F*) gROOT->FindObject("htemp");
   h2->SetLineColor(3);
}