vectorize outer loop
ok, now vectorizing outer loop.
Converting 1000 events now takes 0.8 s (!)
time python convertNanoToHDF5_L1triggerToDeepMET.py -i data/perfNano_TTbar_PU200.110X_set0.root -o data/perfNano_TTbar_PU200.110X_set1.h5 -N 1000
real 0m0.832s
user 0m0.708s
sys 0m0.117s