gr005_apply.py File Reference

A macro to demonstrate the functionality of TGraph.Apply() method.

TGraph.Apply applies a function f to all the data TGraph points, f may be a 1-D function TF1 or 2-d function TF2. The Y values of the graph are replaced by the ROOT.values computed using the function.

The Apply() method can be used as well for TGraphErrors and TGraphAsymmErrors.

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import numpy as np
import ROOT
 
npoints = 3
xaxis = np.array([1.0, 2.0, 3.0])
yaxis = np.array([10.0, 20.0, 30.0])
 
gr1 = ROOT.TGraph(npoints, xaxis, yaxis)
ff = ROOT.TF2("ff", "-1./y")  # Defining the function `f`
 
c1 = ROOT.TCanvas("c1", "c1", 0, 0, 700, 500)
c1.Divide(2, 1)
 
c1.cd(1)
gr1.DrawClone("A*")  # Using DrawClone to create a copy of the graph in the canvas.
c1.cd(2)
gr1.Apply(ff)  # Applies the function `f` to all the data TGraph points
gr1.Draw("A*")
# Without DrawClone, the modifications to gr1 via Apply(ff) are reflected in the original graph
# displayed in c1 (the two drawn graphs are not independent).

Author

Miro Helbich, Jamie Gooding

Definition in file gr005_apply.py.