PyROOT Exercise 3: Canvas and Legends

Exercise

Write a python macro ExerciseCanvas.py.

1. Create two histograms with 50 bins ranging from -3 to 3 with two different names.
2. Fill first histogram with Gaussian distribution with 10000 entries.
3. Fill second histogram with a second order polynomial and 5000 entries (hint: hist2.FillRandom("pol2", 500)).
4. Set the line color of the first histogram to kRed and second to kBlue.
5. Draw both histograms on a canvas.
6. Clone both histograms and normalise them (scale with inverse of the integral).
7. Draw both histograms on a different canvas.
8. Draw a legend on both canvases at position (0.16, 0.63, 0.45, 0.91); bonus: do it after you created both canvases.
9. Save both canvases in a PDF; bonus: save them in the same file.

Solution

import ROOT
%jsroot on

Welcome to JupyROOT 6.28/00

from ROOT import gStyle, TCanvas, TH1D, TLegend, kRed, kBlue

gStyle.SetOptStat(0)

canvas1 = TCanvas("canvas1", "", 800, 600)

hist1 = TH1D("hist1", "Gauss", 50, -3, 3)
hist2 = TH1D("hist2", "Polynomial", 50, -3, 3)

hist1.FillRandom("gaus", 10000)
hist2.FillRandom("pol2", 5000)

hist1.SetLineColor(kRed)
hist2.SetLineColor(kBlue)

hist1.Draw()
hist2.Draw("same")

canvas2 = TCanvas("canvas2", "", 800, 600)

hist1_norm = hist1.Clone("hist1_norm")
hist1_norm.Scale(1 / hist1.Integral())
hist2_norm = hist2.Clone("hist2_norm")
hist2_norm.Scale(1 / hist2.Integral())

hist1_norm.Draw("hist")
hist2_norm.Draw("hist same")

legend = TLegend(0.7, 0.75, 0.90, 0.87)
legend.AddEntry(hist1, hist1.GetTitle(), "l")
legend.AddEntry(hist2, hist2.GetTitle(), "l")
legend.SetBorderSize(0)

canvas1.cd()
legend.Draw()
canvas2.cd()
legend.Draw()

canvas1.Draw()
canvas2.Draw()

canvas1.SaveAs("output.pdf(")
canvas2.SaveAs("output.pdf)")

Info in <TCanvas::Print>: pdf file output.pdf has been created using the current canvas
Info in <TCanvas::Print>: Current canvas added to pdf file output.pdf and file closed

Last update: 06 March 2023