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df_summ = df.groupby(['Airline','AirportFrom','AirportTo'], as_index=False)['id'].agg('count')
df_summ.sort_values(by='id', ascending = False)
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# 22. Summarise and sort
df_summ = df.groupby(['Airline','AirportFrom','AirportTo'], as_index=False)['id'].agg('count')
df_summ.sort_values(by='id', ascending = False)