第一个

选项#1

为值引入一个虚拟列并使用pivot()：

import calendar
weekdays = list(calendar.day_name)

df = pd.DataFrame({'buyer': ['A', 'A', 'B', 'B', 'B', 'C'],
                   'weekday': ['Saturday', 'Friday', 'Monday', 'Tuesday', 'Thursday', 'Monday']})

df["dummy"] = "Y"

df = df.pivot(index="buyer", columns="weekday", values="dummy").reindex(labels=weekdays, axis=1).fillna("").reset_index().rename_axis(columns={"weekday": ""})

[Out]:
  buyer Monday Tuesday Wednesday Thursday Friday Saturday Sunday
0     A                                        Y        Y       
1     B      Y       Y                  Y                       
2     C      Y

选项2

使用groupby、size和unstack的组合，最后使用replace值：

import calendar
weekdays = list(calendar.day_name)

df = pd.DataFrame({'buyer': ['A', 'A', 'B', 'B', 'B', 'C'],
                   'weekday': ['Saturday', 'Friday', 'Monday', 'Tuesday', 'Thursday', 'Monday']})

df = df = df.groupby(["buyer", "weekday"]).size().unstack(fill_value=0).replace({1:"Y",0:""}).reindex(labels=weekdays, axis=1).fillna("").reset_index().rename_axis(columns={"weekday": ""})

[Out]:
  buyer Monday Tuesday Wednesday Thursday Friday Saturday Sunday
0     A                                        Y        Y       
1     B      Y       Y                  Y                       
2     C      Y