There is a Pandas dataframe: year date route operator group_name bus_garage bus_park injury_result incident_type victim_category victim_sex victim_age 0 2015 01.01.2015 1 London General Go-Ahead Garage Not Available Southwark Injuries treated on scene Onboard Injuries Passenger Male Child 1 2015 01.01.2015 4 Metroline Metroline Garage Not Available Islington Injuries treated on scene Onboard Injuries Passenger Male Unknown 2 2015 01.01.2015 5 East London Stagecoach Garage Not Available Havering Taken to Hospital – Reported Serious Injury or... Onboard Injuries Passenger Male Elderly Write a grouped_operators function that groups all values by operator column and sums all dates for each unique operator value

def grouped_operators(df):
  return df.groupby(["operator"])["date"].sum()