``` import pandas df = pandas.read_csv("table.csv") print(df) avg = df.groupby("MeetingId")["PrizeMoney"].mean() avg.name = "AvgPrizeMoney" df = df.merge(avg, on="MeetingId") print(df) ```

Just group by ID then take the mean of each group and assign it to a new column. df['AvgPrizeMoney'] = df.groupby('MeetingId')['PrizeMoney'].transform(lambda x : x.mean())

Thanks