The good old X-axis range problem

[SJLPHI]

Hello,
I am sure that I’ve ran into this problem before and I have not yet found a viable solution, some related posts are here:
https://root.cern.ch/root/roottalk/roottalk99/2603.html
https://root.cern.ch/root/roottalk/roottalk02/4284.html
https://root.cern.ch/root/roottalk/roottalk99/2604.html
https://root.cern.ch/root/roottalk/roottalk04/0934.html
https://root.cern.ch/how/how-set-ranges-axis

I’ve seen many replies that actually do not solve the problem apparently since ROOT3.

Bottom line, I have not yet seen a solution. I’ll describe the situation.

I have a TH1 in a root file.
TFile* file=…
TH1* dummyhist=(TH1*)file->Get(…);

Now, this dummy histogram has values from -15000 to 50000, but I only care about seeing 0 to 3000.

I’ve tried
dummyhist->GetXaxis()->SetRange/SetRangeUser (nothing)
dummyhist->GetXaxis()->SetLimits (label changes but not the position of actual values).

I cannot think of a way to resolve other than to redeclare:
TH1* dummy2=new TH1(“contents and binning as demanded”)
for… fill dummy 1 elements into dummy 2 with significant over/underflow

Does anyone have real a solution for this?

---

_ROOT Version:6.14.0.
Platform: Not Provided
Compiler: Not Provided

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[dastudillo]

The following works for me, right after opening hsimple.root on ROOT 6.16.00

root [1] hpx->Draw()
Info in <TCanvas::MakeDefCanvas>:  created default TCanvas with name c1
root [2] hpx->GetXaxis()->SetRangeUser(0,2)
root [3] gPad->Modified()
root [4] 

Note that before doing gPad->Modified() you don’t see the changes.
Having said that, I have also found cases when no matter how many Modifieds or Updates on pads or canvases, the axis doesn’t change, so I’m not very sure what’s going on

[SJLPHI]

Thank you dastudillo.
I am half-successful with this method. I don’t know why but the histogram shifts 0 just fine, but the upper range seems limited to the maximum of the data.

[jfcaron]

I’m pretty sure you can’t SetRange(User) beyond the range of actual bins in the histogram. The reasoning could be that that would misrepresent the under/overflow bin contents. If you want a very “zoomed out” view you need to make a histogram with bins that go as far as you want to see.

FWIW: I usually make my histograms with a much larger range than necessary, and later constrain the range to only have the bins which have nonzero content. The TH1 methods “FindFirstBinAbove” and “FindLastBinAbove” are useful for this.

[SJLPHI]

I’m currently using what I call a ghosthist method
TF1* ghosthist= new TF1(“ghost”, range that I want);
ghosthist->SetTitle(dummyhist->GetTitle() )
… Take out the properties
ghosthist->Draw();
dummyhist->Draw(“same”);

[SJLPHI]

I should also add that I am just writing a constructor to generalize these, so I can use it easier next time.
Something like

TH1* shift_Histogram(TH1* input hist){
TH1* shifted_histogram
...
return shifted_histogram
}

void draw_shifted_Histogram(TH1* input hist, double xmin, double xmax){
TH1* ghost= new TH1(new range)
ghost->Draw()
input_hist->Draw(“same”)
}

…

I am wondering why the ROOT maintainers haven’t provided such constructors yet.

On request, I can provide the header and cxx ready to be compiled into ROOT.

[couet]

SetRangeUser cannot extend the range beyond the histogram limits.
May be this can help:
https://root.cern.ch/doc/master/classTH1.html#ad467e2133c1dff95f21033a4940beabb

[SJLPHI]

Thank you couet. I am aware of the master document for the class.

I am just pointing out an existing deficiency in ROOT which hasn’t been resolved in a decade…

[couet]

May be @moneta can comment.

[Wile_E_Coyote]

Setting Axis Range Exactly With Variable Bins

You could create and draw an empty histogram, with sufficiently dense x-bins. And then, on top of it, you could draw your “hist” using “same”: { Double_t x[] = {0., 100., 150., 200., 500., 20000.}; TH1F *hist = new TH1F("hist", "hist title;x axis name;y axis name", ((sizeof(x) / sizeof(Double_t)) - 1), x); hist->SetLineColor(kRed); hist->Fill(0., 1.); hist->Fill(100., 2.); hist->Fill(150., 3.); hist->Fill(200., 4.); hist->Fill(500., 5.); // TH1C *h = new TH1C…

[SJLPHI]

Thank you Wlie_E_Coyote, I use the “ghost histogram” in very much the same manner.