Combination of mc21 ttbar samples in preprocessing
The mc21 nominal ttbar MC is split into a 1lepton + jets and a 2-lepton sample, which need to be combined.
It could be implemented as part of the umami preprocessing to take care of the correct merging on event-level basis of the two samples.
In Run-3 MC, a different approach was taken for the ttbar sample than in Run-2 MC. While the Run-2 sample contains all non-allhadronic ttbar processes (1-lepton and di-lepton together), the Run-3 sample is split between these processes. Consequently, you need to merge the two samples in a ratio 5:1. The correct approach is to merge them on event-level basis. As in the h5 file, individual jets are dumped as entries, this requires a more involved procedure by looking at eventnumbers. A script for merging events in this correct procedure is provided here as a gitlab snippet.