How to plot Graph from root file

[Fredrih]

I want to access the graph from the root file to then get the maximum value on the Y axis. After digging in the forum, I managed to write this code. What should be added or removed here?

c = ROOT.TCanvas()
myfile = ROOT.TFile.Open(“/home/erg/2022.12/2022.12.01/Dec01031235.root”)
tree = myfile.Get(“FADCData 939”)
tree.Draw(“Channel1”)
g = ROOT.TGraph()
g = g.gPad.GetPrimitive(“Graph”)
print(ROOT.TMath.MaxElement(10230, g.GetY()))

ROOT Version: Not Provided
Platform: Not Provided
Compiler: Not Provided

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[yus]

Hi,

your

tree.Draw("Channel1")

produces a histogram, not a TGraph.

[Fredrih]

I tried something new. But it gives an empty canvas.

c = ROOT.TCanvas()
f = ROOT.TFile(“/home/erg/2022.12/2022.12.01/Dec01031235.root”)
tree = f.Get(“FADCData 939”)
g = ROOT.TGraph()
g = tree.GetBranch(“Channel1”)
g.Draw()

[yus]

Let’s simplify a bit. Why do you need a TGraph? Why does not a TH1 suffice?

[Fredrih]

I used to think I was working with histograms too. I even made a code that allows you to get their maximums. But some of the values were different from the true ones. Recently I realized that I am dealing with graphs with time on the X axis. However, tree.Draw() produces the same images as when calling rootbrowse. Now I need to write a program that will output all the correct values of the maxima. I attach a file here.
Dec01031235.root (120.3 KB)

[yus]

Then it is something like this:

c = ROOT.TCanvas()
f = ROOT.TFile("Dec01031235.root")
tree = f.Get("FADCData 939")
tree.Draw("Channel1")
myh = ROOT.gPad.GetPrimitive("htemp");
print "Maximum of the histogram is", myh.GetMaximum()

[Fredrih]

Thank you very much, sir! You’ve helped me a lot! Now you can save a lot of time when processing files.