your suggestions of 7/2/19 helped quite a bit wrt to rdf. thanks.
however i am still missing something in one of the examples you gave.
i am using root 6.18 now.
df = df.Filter("nMuon > 0 && nElectron > 0", "Select only valid events")\ .Define("idx", "Combinations(Muon_phi, Electron_phi)")\ .Define("dR", "DeltaR(Take(Muon_phi, idx), Take(Electron_phi, idx),\ Take(Muon_eta,idx)"), Take(Electron_eta,idx)) .Define("minIdx", "ArgMin(dR)")\ .Define("dRMin", "dR[minIdx]") so lets say i have 2 muons and 2 electrons, and i am trying to find the smallest dR between the combinations. a. i am not sure what the idx should be with the Takes in defining DeltaR. i want to loop over all the possible combinations and i dont think the way i defined dR does that. or am i wrong? thanks..kj