RDataFrame in python loop


I heard that RDataFrame is much efficient than classic loops, but I’m not sure how to use it for a simple code as in python:

chain = ROOT.TChain()
h = ROOT.TH1D(“h”,"", n, x_min, x_max)
lvmu2 =ROOT.TLorentzVector()
for ev in chain:
lvmu1.SetPtEtaPhiE(ev.pt_muon[0], ev.eta_muon[0], ev.phi_muon[0], ev.E_muon[0])
lvmu2.SetPtEtaPhiE(ev.pt_muon[1], ev.eta_muon[1], ev.phi_muon[1], ev.E_muon[1])
lvmu3 = lvmu1+ lvmu2

From your example, it’s not clear to understand what you’re trying to do, but maybe @etejedor can help you

Hi Bertrand! I’m trying to fill a histogram with a calculated transverse momentum from the sum of two vectors


Please have a look at the RDataFrame docs first:


With RDataFrame, you don’t iterate over the events explictly (this is hidden inside RDataFrame and done much more efficiently in C++). You proceed by applying per-event transformations to your dataset and finally obtaining some results from it.

In your code, you would construct an RDataFrame from your dataset, then for example define a new column pt from a function that does the per-event calculation you posted here. After that, you would call a Histo1D action on that column.