df017_vecOpsHEP.py

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## \file
## \ingroup tutorial_dataframe
## \notebook -draw
## Use RVecs to plot the transverse momentum of selected particles.
##
## This tutorial shows how VecOps can be used to slim down the programming
## model typically adopted in HEP for analysis.
## In this case we have a dataset containing the kinematic properties of
## particles stored in individual arrays.
## We want to plot the transverse momentum of these particles if the energy is
## greater than 100 MeV.
 
## \macro_code
## \macro_image
##
## \date March 2018
## \authors Danilo Piparo (CERN), Andre Vieira Silva
 
import ROOT
 
filename = ROOT.gROOT.GetTutorialDir().Data() + "/dataframe/df017_vecOpsHEP.root"
treename = "myDataset"
 
def WithPyROOT(filename):
    from math import sqrt
    f = ROOT.TFile(filename)
    h = ROOT.TH1F("pt", "With PyROOT", 16, 0, 4)
    for event in f.myDataset:
        for E, px, py in zip(event.E, event.px, event.py):
            if (E > 100):
               h.Fill(sqrt(px*px + py*py))
    h.DrawCopy()
 
def WithRDataFrameVecOpsJit(treename, filename):
    f = ROOT.RDataFrame(treename, filename)
    h = f.Define("good_pt", "sqrt(px*px + py*py)[E>100]")\
         .Histo1D(("pt", "With RDataFrame and RVec", 16, 0, 4), "good_pt")
    h.DrawCopy()
 
## We plot twice the same quantity, the key is to look into the implementation
## of the functions above.
c = ROOT.TCanvas()
c.Divide(2,1)
c.cd(1)
WithPyROOT(filename)
c.cd(2)
WithRDataFrameVecOpsJit(treename, filename)
c.SaveAs("df017_vecOpsHEP.png")
 
print("Saved figure to df017_vecOpsHEP.png")